diff --git a/poetry.lock b/poetry.lock
index 4969431..6f68ed7 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -123,7 +123,7 @@ name = "cachecontrol"
 version = "0.12.6"
 description = "httplib2 caching for requests"
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [package.dependencies]
@@ -148,7 +148,7 @@ name = "cachy"
 version = "0.3.0"
 description = "Cachy provides a simple yet effective caching library."
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [package.extras]
@@ -169,7 +169,7 @@ name = "cffi"
 version = "1.14.4"
 description = "Foreign Function Interface for Python calling C code."
 category = "main"
-optional = false
+optional = true
 python-versions = "*"
 
 [package.dependencies]
@@ -196,7 +196,7 @@ name = "cleo"
 version = "0.8.1"
 description = "Cleo allows you to create beautiful and testable command-line interfaces."
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [package.dependencies]
@@ -215,7 +215,7 @@ name = "clikit"
 version = "0.6.2"
 description = "CliKit is a group of utilities to build beautiful and testable command line interfaces."
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [package.dependencies]
@@ -247,7 +247,7 @@ name = "crashtest"
 version = "0.3.1"
 description = "Manage Python errors with ease"
 category = "main"
-optional = false
+optional = true
 python-versions = ">=3.6,<4.0"
 
 [[package]]
@@ -255,7 +255,7 @@ name = "cryptography"
 version = "3.2.1"
 description = "cryptography is a package which provides cryptographic recipes and primitives to Python developers."
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*"
 
 [package.dependencies]
@@ -263,11 +263,11 @@ cffi = ">=1.8,<1.11.3 || >1.11.3"
 six = ">=1.4.1"
 
 [package.extras]
-docs = ["sphinx (>=1.6.5,<1.8.0 || >1.8.0,<3.1.0 || >3.1.0,<3.1.1 || >3.1.1)", "sphinx-rtd-theme"]
+docs = ["sphinx (>=1.6.5,!=1.8.0,!=3.1.0,!=3.1.1)", "sphinx-rtd-theme"]
 docstest = ["doc8", "pyenchant (>=1.6.11)", "twine (>=1.12.0)", "sphinxcontrib-spelling (>=4.0.1)"]
 pep8test = ["black", "flake8", "flake8-import-order", "pep8-naming"]
 ssh = ["bcrypt (>=3.1.5)"]
-test = ["pytest (>=3.6.0,<3.9.0 || >3.9.0,<3.9.1 || >3.9.1,<3.9.2 || >3.9.2)", "pretend", "iso8601", "pytz", "hypothesis (>=1.11.4,<3.79.2 || >3.79.2)"]
+test = ["pytest (>=3.6.0,!=3.9.0,!=3.9.1,!=3.9.2)", "pretend", "iso8601", "pytz", "hypothesis (>=1.11.4,!=3.79.2)"]
 
 [[package]]
 name = "dataclasses"
@@ -344,7 +344,7 @@ name = "html5lib"
 version = "1.1"
 description = "HTML parser based on the WHATWG HTML specification"
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
 
 [package.dependencies]
@@ -477,7 +477,7 @@ python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
 parso = ">=0.7.0,<0.8.0"
 
 [package.extras]
-qa = ["flake8 (3.7.9)"]
+qa = ["flake8 (==3.7.9)"]
 testing = ["Django (<3.1)", "colorama", "docopt", "pytest (>=3.9.0,<5.0.0)"]
 
 [[package]]
@@ -485,7 +485,7 @@ name = "jeepney"
 version = "0.6.0"
 description = "Low-level, pure Python DBus protocol wrapper."
 category = "main"
-optional = false
+optional = true
 python-versions = ">=3.6"
 
 [package.extras]
@@ -496,7 +496,7 @@ name = "keyring"
 version = "21.5.0"
 description = "Store and access your passwords safely."
 category = "main"
-optional = false
+optional = true
 python-versions = ">=3.6"
 
 [package.dependencies]
@@ -507,7 +507,7 @@ SecretStorage = {version = ">=3.2", markers = "sys_platform == \"linux\""}
 
 [package.extras]
 docs = ["sphinx", "jaraco.packaging (>=3.2)", "rst.linker (>=1.9)"]
-testing = ["pytest (>=3.5,<3.7.3 || >3.7.3)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "jaraco.test (>=3.2.0)", "pytest-black (>=0.3.7)", "pytest-mypy"]
+testing = ["pytest (>=3.5,!=3.7.3)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "jaraco.test (>=3.2.0)", "pytest-black (>=0.3.7)", "pytest-mypy"]
 
 [[package]]
 name = "lazy-object-proxy"
@@ -522,7 +522,7 @@ name = "lockfile"
 version = "0.12.2"
 description = "Platform-independent file locking module"
 category = "main"
-optional = false
+optional = true
 python-versions = "*"
 
 [[package]]
@@ -538,7 +538,7 @@ name = "msgpack"
 version = "1.0.0"
 description = "MessagePack (de)serializer."
 category = "main"
-optional = false
+optional = true
 python-versions = "*"
 
 [[package]]
@@ -601,7 +601,7 @@ name = "pastel"
 version = "0.2.1"
 description = "Bring colors to your terminal."
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [[package]]
@@ -644,7 +644,7 @@ name = "pkginfo"
 version = "1.6.1"
 description = "Query metadatdata from sdists / bdists / installed packages."
 category = "main"
-optional = false
+optional = true
 python-versions = "*"
 
 [package.extras]
@@ -669,7 +669,7 @@ name = "poetry"
 version = "1.1.4"
 description = "Python dependency management and packaging made easy."
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
 
 [package.dependencies]
@@ -764,7 +764,7 @@ name = "pycparser"
 version = "2.20"
 description = "C parser in Python"
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [[package]]
@@ -780,7 +780,7 @@ name = "pylev"
 version = "1.3.0"
 description = "A pure Python Levenshtein implementation that's not freaking GPL'd."
 category = "main"
-optional = false
+optional = true
 python-versions = "*"
 
 [[package]]
@@ -826,7 +826,7 @@ py = ">=1.8.2"
 toml = "*"
 
 [package.extras]
-checkqa_mypy = ["mypy (0.780)"]
+checkqa_mypy = ["mypy (==0.780)"]
 testing = ["argcomplete", "hypothesis (>=3.56)", "mock", "nose", "requests", "xmlschema"]
 
 [[package]]
@@ -842,14 +842,14 @@ coverage = ">=4.4"
 pytest = ">=4.6"
 
 [package.extras]
-testing = ["fields", "hunter", "process-tests (2.0.2)", "six", "pytest-xdist", "virtualenv"]
+testing = ["fields", "hunter", "process-tests (==2.0.2)", "six", "pytest-xdist", "virtualenv"]
 
 [[package]]
 name = "pywin32-ctypes"
 version = "0.2.0"
 description = ""
 category = "main"
-optional = false
+optional = true
 python-versions = "*"
 
 [[package]]
@@ -895,14 +895,14 @@ urllib3 = ">=1.21.1,<1.27"
 
 [package.extras]
 security = ["pyOpenSSL (>=0.14)", "cryptography (>=1.3.4)"]
-socks = ["PySocks (>=1.5.6,<1.5.7 || >1.5.7)", "win-inet-pton"]
+socks = ["PySocks (>=1.5.6,!=1.5.7)", "win-inet-pton"]
 
 [[package]]
 name = "requests-toolbelt"
 version = "0.9.1"
 description = "A utility belt for advanced users of python-requests"
 category = "main"
-optional = false
+optional = true
 python-versions = "*"
 
 [package.dependencies]
@@ -950,7 +950,7 @@ name = "secretstorage"
 version = "3.3.0"
 description = "Python bindings to FreeDesktop.org Secret Service API"
 category = "main"
-optional = false
+optional = true
 python-versions = ">=3.6"
 
 [package.dependencies]
@@ -962,7 +962,7 @@ name = "shellingham"
 version = "1.3.2"
 description = "Tool to Detect Surrounding Shell"
 category = "main"
-optional = false
+optional = true
 python-versions = "!=3.0,!=3.1,!=3.2,!=3.3,>=2.6"
 
 [[package]]
@@ -1006,7 +1006,7 @@ name = "tomlkit"
 version = "0.7.0"
 description = "Style preserving TOML library"
 category = "main"
-optional = false
+optional = true
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
 
 [[package]]
@@ -1073,7 +1073,7 @@ python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, <4"
 [package.extras]
 brotli = ["brotlipy (>=0.6.0)"]
 secure = ["pyOpenSSL (>=0.14)", "cryptography (>=1.3.4)", "idna (>=2.0.0)", "certifi", "ipaddress"]
-socks = ["PySocks (>=1.5.6,<1.5.7 || >1.5.7,<2.0)"]
+socks = ["PySocks (>=1.5.6,!=1.5.7,<2.0)"]
 
 [[package]]
 name = "virtualenv"
@@ -1108,7 +1108,7 @@ name = "webencodings"
 version = "0.5.1"
 description = "Character encoding aliases for legacy web content"
 category = "main"
-optional = false
+optional = true
 python-versions = "*"
 
 [[package]]
@@ -1129,12 +1129,12 @@ python-versions = ">=3.6"
 
 [package.extras]
 docs = ["sphinx", "jaraco.packaging (>=3.2)", "rst.linker (>=1.9)"]
-testing = ["pytest (>=3.5,<3.7.3 || >3.7.3)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "jaraco.test (>=3.2.0)", "jaraco.itertools", "func-timeout", "pytest-black (>=0.3.7)", "pytest-mypy"]
+testing = ["pytest (>=3.5,!=3.7.3)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "jaraco.test (>=3.2.0)", "jaraco.itertools", "func-timeout", "pytest-black (>=0.3.7)", "pytest-mypy"]
 
 [metadata]
 lock-version = "1.1"
 python-versions = "^3.6.1"
-content-hash = "8eea42cb6c60df03376bb264b444ccd0a63a211122edc6625284d57204295273"
+content-hash = "b466984a069123fa9c5af59c37a6a8c8404742eb90a45c37fc6d73d87e6383f8"
 
 [metadata.files]
 appdirs = [
diff --git a/pyproject.toml b/pyproject.toml
index 34ee599..6efee11 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -32,11 +32,14 @@ classifiers = [
 [tool.poetry.plugins.tox]
 poetry_installer = "tox_poetry_installer"
 
+[tool.poetry.extras]
+poetry = ["poetry"]
+
 [tool.poetry.dependencies]
 python = "^3.6.1"
-poetry = "^1.0.0"
+poetry = {version = "^1.0.0", optional = true}
 poetry-core = "^1.0.0"
-tox = "^2.3.0 || ^3.0.0"
+tox = "^3.0.0"
 
 [tool.poetry.dev-dependencies]
 bandit = "^1.6.2"