Bump bleach from 3.1.1 to 3.1.2 in /docs

Bumps [bleach](https://github.com/mozilla/bleach) from 3.1.1 to 3.1.2.
- [Release notes](https://github.com/mozilla/bleach/releases)
- [Changelog](https://github.com/mozilla/bleach/blob/master/CHANGES)
- [Commits](mozilla/bleach@v3.1.1...v3.1.2)

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,6 +1,6 @@
 alabaster==0.7.12
 Babel==2.7.0
-bleach==3.1.1
+bleach==3.1.2
 certifi==2019.11.28
 chardet==3.0.4
 coverage==4.5.4