Bump alabaster from 0.7.12 to 0.7.13

Bumps [alabaster](https://github.com/sphinx-doc/alabaster) from 0.7.12 to 0.7.13.
- [Release notes](https://github.com/sphinx-doc/alabaster/releases)
- [Changelog](https://github.com/sphinx-doc/alabaster/blob/master/docs/changelog.rst)
- [Commits](sphinx-doc/alabaster@0.7.12...0.7.13)

---
updated-dependencies:
- dependency-name: alabaster
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

requirements-transitive.txt

@@ -4,7 +4,7 @@
 # See install_requires and extras_require in setup.py for the range of versions
 # supported.
 advocate==1.0.0
-alabaster==0.7.12
+alabaster==0.7.13
 amqp==5.2.0
 appdirs==1.4.4
 aspy.refactor-imports==2.1.1