Added python3.9 to tox

Author: dany74q

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{36,37,38}-{darwin,linux,win32}
+envlist = py{36,37,38,39}-{darwin,linux,win32}
 minversion = 3.20.0
 requires =
     tox-pip-version>=0.0.7
@@ -10,7 +10,8 @@ requires =
 python =
     3.6: py36
     3.7: py37
-    3.8: py38, docs, build, release
+    3.8: py38
+    3.9: py39, docs, build, release
 
 [testenv]
 platform =