Bump blacken-docs from 1.9.1 to 1.10.0 (#142)

Bumps [blacken-docs](https://github.com/asottile/blacken-docs) from 1.9.1 to 1.10.0.
- [Release notes](https://github.com/asottile/blacken-docs/releases)
- [Commits](adamchainz/blacken-docs@v1.9.1...v1.10.0)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements_dev.txt

@@ -1,5 +1,5 @@
 black==21.4b0
-blacken-docs==1.9.1
+blacken-docs==1.10.0
 pip==21.1.2
 pre-commit==2.13.0
 twine==3.3.0