Bump blacken-docs from 1.12.0 to 1.14.0

Bumps [blacken-docs](https://github.com/asottile/blacken-docs) from 1.12.0 to 1.14.0.
- [Changelog](https://github.com/adamchainz/blacken-docs/blob/main/CHANGELOG.rst)
- [Commits](adamchainz/blacken-docs@v1.12.0...1.14.0)

---
updated-dependencies:
- dependency-name: blacken-docs
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

requirements_dev.txt

@@ -1,6 +1,6 @@
 autopep8==1.6.0
 black==21.12b0
-blacken-docs==1.12.0
+blacken-docs==1.14.0
 pip==21.3.1
 pre-commit==2.16.0
 twine==4.0.2