Bump bleach from 3.1.0 to 3.1.2

Bumps [bleach](https://github.com/mozilla/bleach) from 3.1.0 to 3.1.2.
- [Release notes](https://github.com/mozilla/bleach/releases)
- [Changelog](https://github.com/mozilla/bleach/blob/master/CHANGES)
- [Commits](mozilla/bleach@v3.1.0...v3.1.2)

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

requirements.txt

@@ -7,7 +7,7 @@ Babel==2.7.0
 backcall==0.1.0
 backports.functools-lru-cache==1.6.1
 biblib-simple==0.1.1
-bleach==3.1.0
+bleach==3.1.2
 certifi==2019.9.11
 cfgv==2.0.1
 chardet==3.0.4