chore(deps): bump bleach from 3.1.0 to 3.1.1 in /requirements

Bumps [bleach](https://github.com/mozilla/bleach) from 3.1.0 to 3.1.1.
- [Release notes](https://github.com/mozilla/bleach/releases)
- [Changelog](https://github.com/mozilla/bleach/blob/master/CHANGES)
- [Commits](mozilla/bleach@v3.1.0...v3.1.1)

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

requirements/base.txt

@@ -16,7 +16,7 @@ wagtail==2.6.2
 whitenoise==4.1.4
 
 # Inherited a4-core requirements
-bleach==3.1.0
+bleach==3.1.1
 Django==2.2.9 # pyup: <2.3
 django-allauth==0.40.0
 django-autoslug==1.9.6