Bump nokogiri from 1.10.4 to 1.10.8 in /docs (#63)

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.10.4 to 1.10.8.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sparklemotion/nokogiri/compare/v1.10.4...v1.10.8)

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

Co-authored-by: Mattia Iavarone <mat.iavarone@gmail.com>