Bump bleach from 2.1.4 to 3.1.2

Bumps [bleach](https://github.com/mozilla/bleach) from 2.1.4 to 3.1.2.
- [Release notes](https://github.com/mozilla/bleach/releases)
- [Changelog](https://github.com/mozilla/bleach/blob/master/CHANGES)
- [Commits](mozilla/bleach@v2.1.4...v3.1.2)

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

requirements.txt

@@ -2,7 +2,7 @@ astroid==2.0.4
 atomicwrites==1.2.1
 attrs==18.2.0
 autopep8==1.4
-bleach==2.1.4
+bleach==3.1.2
 certifi==2018.8.24
 cffi==1.11.5
 chardet==3.0.4