Add missing entry to tox config.
@@ -19,6 +19,7 @@ basepython =
py3.5: python3.5
py3.6: python3.6
{py3.7,checks,lint,pylint,mypy,coverage,docs,py3.7-dist}: python3.7
+ py3.8: python3.8
mypy: python3.7
whitelist_externals = cp
bash
