Bump bleach from 1.5.0 to 3.1.1

Bumps [bleach](https://github.com/mozilla/bleach) from 1.5.0 to 3.1.1.
- [Release notes](https://github.com/mozilla/bleach/releases)
- [Changelog](https://github.com/mozilla/bleach/blob/master/CHANGES)
- [Commits](mozilla/bleach@v1.5...v3.1.1)

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

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 absl-py==0.7.1
 astor==0.7.1
 backports.weakref==1.0rc1
-bleach==1.5.0
+bleach==3.1.1
 cycler==0.10.0
 gast==0.2.2
 grpcio==1.20.0