Bump nokogiri from 1.10.1 to 1.10.4 in /docs

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.10.1 to 1.10.4.
- [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/v1.10.1...v1.10.4)

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