Bump pydocstyle from 5.1.1 to 6.0.0 (#69)

Bumps [pydocstyle](https://github.com/PyCQA/pydocstyle) from 5.1.1 to 6.0.0.
- [Release notes](https://github.com/PyCQA/pydocstyle/releases)
- [Changelog](https://github.com/PyCQA/pydocstyle/blob/master/docs/release_notes.rst)
- [Commits](PyCQA/pydocstyle@5.1.1...6.0.0)

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