Bump mypy from 0.800 to 0.812 (#63)

Bumps [mypy](https://github.com/python/mypy) from 0.800 to 0.812.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.800...v0.812)

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Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

poetry.lock

@@ -46,7 +46,7 @@ python = "^3.6"
 typing-extensions = "^3.7"
 
 [tool.poetry.dev-dependencies]
-mypy = "^0.800"
+mypy = "^0.812"
 wemake-python-styleguide = "^0.15.1"
 flake8-pytest = "^1.3"
 flake8-pytest-style = "^1.3.0"