Bump flake8-docstrings from 1.5.0 to 1.6.0

Bumps [flake8-docstrings](https://gitlab.com/pycqa/flake8-docstrings) from 1.5.0 to 1.6.0.
- [Release notes](https://gitlab.com/pycqa/flake8-docstrings/tags)
- [Changelog](https://gitlab.com/pycqa/flake8-docstrings/blob/master/HISTORY.rst)
- [Commits](https://gitlab.com/pycqa/flake8-docstrings/compare/1.5.0...1.6.0

)

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