Add python 3.8 to CI

.github/workflows/pull_request.yml

@@ -7,7 +7,7 @@ jobs:
     strategy:
       max-parallel: 2
       matrix:
-        python-version: [3.6, 3.7]
+        python-version: [3.6, 3.7, 3.8]
     steps:
     - uses: actions/checkout@master
     - name: Set up Python ${{ matrix.python-version }}

tox.ini

@@ -3,11 +3,12 @@
 [tox]
 envlist =
     check,
-    {py3.7,py3.6},
+    {py3.8,py3.7,py3.6},
     docs
 
 [testenv]
 basepython =
+    py3.8: {env:TOXPYTHON:python3.8}
     py3.7: {env:TOXPYTHON:python3.7}
     py3.6: {env:TOXPYTHON:python3.6}
     {bootstrap,check,docs}: {env:TOXPYTHON:python3}