Bump sphinx-rtd-theme from 1.1.1 to 1.2.2

Bumps [sphinx-rtd-theme](https://github.com/readthedocs/sphinx_rtd_theme) from 1.1.1 to 1.2.2.
- [Changelog](https://github.com/readthedocs/sphinx_rtd_theme/blob/master/docs/changelog.rst)
- [Commits](readthedocs/sphinx_rtd_theme@1.1.1...1.2.2)

---
updated-dependencies:
- dependency-name: sphinx-rtd-theme
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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