Update mypy from 0.790 to 0.812 (#503)

Co-authored-by: Abhinav Singh <[email protected]>

Author: pyup-bot

requirements-testing.txt

@@ -4,7 +4,7 @@ flake8==3.8.4
 pytest==6.2.2
 pytest-cov==2.11.1
 autopep8==1.5.5
-mypy==0.790
+mypy==0.812
 py-spy==0.3.3
 codecov==2.1.11
 tox==3.22.0