Bump mypy from 0.790 to 0.812

Bumps [mypy](https://github.com/python/mypy) from 0.790 to 0.812.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.790...v0.812)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements-test.txt

@@ -4,4 +4,4 @@ pytest-cov==2.10.0
 black==19.10b0
 flake8==3.8.4
 isort[pipfile]==5.7.0
-mypy==0.790
+mypy==0.812