build(deps): bump babel from 2.9.0 to 2.9.1 in /docs (#1245)

Bumps [babel](https://github.com/python-babel/babel) from 2.9.0 to 2.9.1.
- [Release notes](https://github.com/python-babel/babel/releases)
- [Changelog](https://github.com/python-babel/babel/blob/master/CHANGES)
- [Commits](python-babel/babel@v2.9.0...v2.9.1)

---
updated-dependencies:
- dependency-name: babel
  dependency-type: direct:production
...

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,5 +1,5 @@
 alabaster==0.7.12
-Babel==2.9.0
+Babel==2.9.1
 certifi==2020.12.5
 chardet==4.0.0
 commonmark==0.9.1