feature: enable python 3.9

Author: mufaddal-rohawala

setup.py

@@ -104,6 +104,7 @@ def read_version():
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
     ],
     install_requires=required_packages,
     extras_require=extras,

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = black-format,flake8,pylint,docstyle,sphinx,doc8,twine,py36,py37,py38
+envlist = black-format,flake8,pylint,docstyle,sphinx,doc8,twine,py36,py37,py38,py39
 
 skip_missing_interpreters = False
 
@@ -72,7 +72,7 @@ commands =
     {env:IGNORE_COVERAGE:} coverage report -i --fail-under=86
 deps = .[test]
 depends =
-    {py36,py37,py38}: clean
+    {py36,py37,py38,py39}: clean
 
 [testenv:flake8]
 skipdist = true