Bump black from 21.10b0 to 21.12b0 (#365)

Bumps [black](https://github.com/psf/black) from 21.10b0 to 21.12b0.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](https://github.com/psf/black/commits)

---
updated-dependencies:
- dependency-name: black
  dependency-type: direct:development
...

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

Author: dependabot[bot]

requirements-dev.txt

@@ -6,4 +6,4 @@ sphinx>=2
 sphinx_rtd_theme
 pypandoc
 twine
-black==21.10b0
+black==21.12b0