Bump babel from 2.7.0 to 2.9.1 in /requirements

Bumps [babel](https://github.com/python-babel/babel) from 2.7.0 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@v2.7.0...v2.9.1)

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

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

Author: dependabot[bot]

requirements/common.txt

@@ -1,7 +1,7 @@
 amqp==2.5.1
 arrow==0.14.2
 asn1crypto==0.24.0
-Babel==2.7.0
+Babel==2.9.1
 bcrypt==3.1.6
 beautifulsoup4==4.7.1
 bibtexparser==1.1.0