Bump mypy from 0.780 to 0.781 (#37)

Bumps [mypy](https://github.com/python/mypy) from 0.780 to 0.781.
- [Release notes](https://github.com/python/mypy/releases)
- [Commits](python/mypy@v0.780...v0.781)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 entrypoints==0.3
 flake8==3.8.3
 mccabe==0.6.1
-mypy==0.780
+mypy==0.781
 pycodestyle==2.6.0
 pyflakes==2.2.0
 typed-ast==1.4.1