Bump babel from 2.6.0 to 2.9.1

Bumps [babel](https://github.com/python-babel/babel) from 2.6.0 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@v2.6.0...v2.9.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 -i https://pypi.org/simple
 atomicwrites==1.3.0
 attrs==19.1.0
-babel==2.6.0
+babel==2.9.1
 backports-abc==0.5
 bcrypt==3.1.6
 blinker==1.4