Bump babel from 2.8.0 to 2.9.1

Bumps [babel](https://github.com/python-babel/babel) from 2.8.0 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@v2.8.0...v2.9.1)

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

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

requirements.txt

@@ -3,7 +3,7 @@ AnyQt==0.0.10
 apturl==0.5.2
 asn1crypto==0.24.0
 attrs==19.3.0
-Babel==2.8.0
+Babel==2.9.1
 bleach==3.3.0
 boto==2.49.0
 boto3==1.10.36