Update mypy to 0.780

[pyup-bot]

This PR updates mypy from 0.770 to 0.780.

The bot wasn't able to find a changelog for this release. Got an idea?

Links

• PyPI: https://pypi.org/project/mypy
• Homepage: http://www.mypy-lang.org/

[codecov]

Codecov Report

Merging #357 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #357   +/-   ##
========================================
  Coverage    81.34%   81.34%           
========================================
  Files           72       72           
  Lines         2776     2776           
========================================
  Hits          2258     2258           
  Misses         518      518           

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