[Security] 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. **This update includes security fixes.**
- [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)

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