Update pydocstyle requirement from >=3.0.0 to >=6.3.0 (#159)

Updates the requirements on [pydocstyle](https://github.com/PyCQA/pydocstyle) to permit the latest version.
- [Release notes](https://github.com/PyCQA/pydocstyle/releases)
- [Changelog](https://github.com/PyCQA/pydocstyle/blob/master/docs/release_notes.rst)
- [Commits](PyCQA/pydocstyle@3.0.0...6.3.0)

---
updated-dependencies:
- dependency-name: pydocstyle
  dependency-version: 6.3.0
  dependency-type: direct:development
...

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Author: dependabot[bot]

dev-requirements.txt

@@ -5,4 +5,4 @@ pytest-cov>=2.6.1
 setuptools>=40.8.0
 vulture>=1.0
 bandit>=1.5.1
-pydocstyle>=3.0.0
+pydocstyle>=6.3.0