diff --git a/poetry.lock b/poetry.lock
index 049049b..d3f6f69 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -180,18 +180,18 @@ python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [[package]]
 name = "importlib-metadata"
-version = "3.1.1"
+version = "2.1.1"
 description = "Read metadata from Python packages"
 category = "dev"
 optional = false
-python-versions = ">=3.6"
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,>=2.7"
 
 [package.dependencies]
 zipp = ">=0.5"
 
 [package.extras]
-docs = ["sphinx", "jaraco.packaging (>=3.2)", "rst.linker (>=1.9)"]
-testing = ["pytest (>=3.5,!=3.7.3)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "jaraco.test (>=3.2.0)", "packaging", "pep517", "pyfakefs", "flufl.flake8", "pytest-black (>=0.3.7)", "pytest-mypy", "importlib-resources (>=1.3)"]
+docs = ["sphinx", "rst.linker"]
+testing = ["packaging", "pep517", "unittest2", "importlib-resources (>=1.3)"]
 
 [[package]]
 name = "importlib-resources"
@@ -511,23 +511,26 @@ python-versions = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*"
 
 [[package]]
 name = "tox"
-version = "3.12.1"
+version = "3.20.1"
 description = "tox is a generic virtualenv management and test command line tool"
 category = "dev"
 optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,>=2.7"
 
 [package.dependencies]
-filelock = ">=3.0.0,<4"
-pluggy = ">=0.3.0,<1"
-py = ">=1.4.17,<2"
-six = ">=1.0.0,<2"
+colorama = {version = ">=0.4.1", markers = "platform_system == \"Windows\""}
+filelock = ">=3.0.0"
+importlib-metadata = {version = ">=0.12,<3", markers = "python_version < \"3.8\""}
+packaging = ">=14"
+pluggy = ">=0.12.0"
+py = ">=1.4.17"
+six = ">=1.14.0"
 toml = ">=0.9.4"
-virtualenv = ">=14.0.0"
+virtualenv = ">=16.0.0,<20.0.0 || >20.0.0,<20.0.1 || >20.0.1,<20.0.2 || >20.0.2,<20.0.3 || >20.0.3,<20.0.4 || >20.0.4,<20.0.5 || >20.0.5,<20.0.6 || >20.0.6,<20.0.7 || >20.0.7"
 
 [package.extras]
-docs = ["sphinx (>=2.0.0,<3)", "towncrier (>=18.5.0)", "pygments-github-lexers (>=0.0.5)", "sphinxcontrib-autoprogram (>=0.1.5)"]
-testing = ["freezegun (>=0.3.11,<1)", "pathlib2 (>=2.3.3,<3)", "pytest (>=3.0.0,<5)", "pytest-cov (>=2.5.1,<3)", "pytest-mock (>=1.10.0,<2)", "pytest-xdist (>=1.22.2,<2)", "pytest-randomly (>=1.2.3,<2)", "flaky (>=3.4.0,<4)", "psutil (>=5.6.1,<6)"]
+docs = ["pygments-github-lexers (>=0.0.5)", "sphinx (>=2.0.0)", "sphinxcontrib-autoprogram (>=0.1.5)", "towncrier (>=18.5.0)"]
+testing = ["flaky (>=3.4.0)", "freezegun (>=0.3.11)", "pathlib2 (>=2.3.3)", "psutil (>=5.6.1)", "pytest (>=4.0.0)", "pytest-cov (>=2.5.1)", "pytest-mock (>=1.10.0)", "pytest-randomly (>=1.0.0)", "pytest-xdist (>=1.22.2)"]
 
 [[package]]
 name = "typed-ast"
@@ -712,8 +715,8 @@ idna = [
     {file = "idna-2.10.tar.gz", hash = "sha256:b307872f855b18632ce0c21c5e45be78c0ea7ae4c15c828c20788b26921eb3f6"},
 ]
 importlib-metadata = [
-    {file = "importlib_metadata-3.1.1-py3-none-any.whl", hash = "sha256:6112e21359ef8f344e7178aa5b72dc6e62b38b0d008e6d3cb212c5b84df72013"},
-    {file = "importlib_metadata-3.1.1.tar.gz", hash = "sha256:b0c2d3b226157ae4517d9625decf63591461c66b3a808c2666d538946519d170"},
+    {file = "importlib_metadata-2.1.1-py2.py3-none-any.whl", hash = "sha256:c2d6341ff566f609e89a2acb2db190e5e1d23d5409d6cc8d2fe34d72443876d4"},
+    {file = "importlib_metadata-2.1.1.tar.gz", hash = "sha256:b8de9eff2b35fb037368f28a7df1df4e6436f578fa74423505b6c6a778d5b5dd"},
 ]
 importlib-resources = [
     {file = "importlib_resources-3.3.0-py2.py3-none-any.whl", hash = "sha256:a3d34a8464ce1d5d7c92b0ea4e921e696d86f2aa212e684451cb1482c8d84ed5"},
@@ -910,8 +913,8 @@ toml = [
     {file = "toml-0.10.2.tar.gz", hash = "sha256:b3bda1d108d5dd99f4a20d24d9c348e91c4db7ab1b749200bded2f839ccbe68f"},
 ]
 tox = [
-    {file = "tox-3.12.1-py2.py3-none-any.whl", hash = "sha256:f5c8e446b51edd2ea97df31d4ded8c8b72e7d6c619519da6bb6084b9dd5770f9"},
-    {file = "tox-3.12.1.tar.gz", hash = "sha256:f87fd33892a2df0950e5e034def9468988b8d008c7e9416be665fcc0dd45b14f"},
+    {file = "tox-3.20.1-py2.py3-none-any.whl", hash = "sha256:42ce19ce5dc2f6d6b1fdc5666c476e1f1e2897359b47e0aa3a5b774f335d57c2"},
+    {file = "tox-3.20.1.tar.gz", hash = "sha256:4321052bfe28f9d85082341ca8e233e3ea901fdd14dab8a5d3fbd810269fbaf6"},
 ]
 typed-ast = [
     {file = "typed_ast-1.4.1-cp35-cp35m-manylinux1_i686.whl", hash = "sha256:73d785a950fc82dd2a25897d525d003f6378d1cb23ab305578394694202a58c3"},