Bump mkdocs from 1.1.2 to 1.2.3 (#135)

Bumps [mkdocs](https://github.com/mkdocs/mkdocs) from 1.1.2 to 1.2.3.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](https://github.com/mkdocs/mkdocs/compare/1.1.2...1.2.3)

---
updated-dependencies:
- dependency-name: mkdocs
  dependency-type: indirect
...

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