build(deps): bump unf_ext from 0.0.8 to 0.0.8.1 in /docs

Bumps [unf_ext](https://github.com/knu/ruby-unf_ext) from 0.0.8 to 0.0.8.1.
- [Release notes](https://github.com/knu/ruby-unf_ext/releases)
- [Changelog](https://github.com/knu/ruby-unf_ext/blob/master/CHANGELOG.md)
- [Commits](https://github.com/knu/ruby-unf_ext/compare/v0.0.8...v0.0.8.1)

---
updated-dependencies:
- dependency-name: unf_ext
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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