Add mypy to tox configuration

Now that all very obvious type problems are resolved, mypy can be used
in the static analysis part.

Author: MaxG87

setup.cfg

@@ -3,3 +3,9 @@ universal=1
 
 [aliases]
 test=pytest
+
+[mypy]
+ignore_missing_imports = True
+warn_return_any = True
+warn_unreachable = True
+warn_unused_ignores = True

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = flake8,py36,py37,py38,py39
+envlist = flake8,mypy,py36,py37,py38,py39
 skip_missing_interpreters = True
 
 [testenv]
@@ -15,3 +15,8 @@ usedevelop = True
 [testenv:flake8]
 deps = flake8
 commands = flake8 --show-source watson/ tests/ scripts/
+
+
+[testenv:mypy]
+deps = mypy==0.812
+commands = mypy watson/ tests/ scripts/