Add python 3.10 to ci configuration

Author: hugovk

.github/workflows/test.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.5, 3.6, 3.7, 3.8, 3.9, pypy3]
+        python-version: [3.5, 3.6, 3.7, 3.8, 3.9, 3.10-dev, pypy3]
 
     steps:
       - uses: actions/checkout@v2

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py35,py36,py37,py38,py39,pypy3
+envlist = py35,py36,py37,py38,py39,310,pypy3
 minversion = 1.6
 
 [testenv]