Add python 3.9 support

Author: mayeut

.travis.yml

@@ -7,6 +7,7 @@ jobs:
   - python: "3.6"
   - python: "3.7"
   - python: "3.8"
+  - python: "3.9"
   - python: "3.7"
     arch: arm64
   - python: "3.7"

setup.cfg

@@ -17,6 +17,7 @@ classifier =
         Programming Language :: Python :: 3.6
         Programming Language :: Python :: 3.7
         Programming Language :: Python :: 3.8
+        Programming Language :: Python :: 3.9
         Programming Language :: Python :: 3 :: Only
         Topic :: Software Development
         Topic :: Software Development :: Build Tools

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 minversion = 1.6
 skipsdist = True
-envlist = py36,py37,py38,lint,cov
+envlist = py36,py37,py38,py39,lint,cov
 
 [testenv]
 deps = .