Bump babel from 2.9.0 to 2.9.1

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](https://github.com/python-babel/babel/compare/v2.9.0...v2.9.1)

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -1,5 +1,5 @@
 certifi==2020.12.05
-babel==2.9.0
+babel==2.9.1
 flask-babel==2.0.0
 flask==1.1.2
 jinja2==2.11.3