Bump m2r2 from 0.2.8 to 0.3.1

Bumps [m2r2](https://github.com/crossnox/m2r2) from 0.2.8 to 0.3.1.
- [Release notes](https://github.com/crossnox/m2r2/releases)
- [Changelog](https://github.com/CrossNox/m2r2/blob/development/CHANGES.md)
- [Commits](CrossNox/m2r2@v0.2.8...v0.3.1)

---
updated-dependencies:
- dependency-name: m2r2
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

docs/requirements.txt

@@ -1,3 +1,3 @@
 sphinx==4.0.2
 sphinx_rtd_theme==0.5.2
-m2r2==0.2.8
+m2r2==0.3.1