Bump nokogiri from 1.13.3 to 1.13.4 in /docs

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.13.3 to 1.13.4.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/v1.13.4/CHANGELOG.md)
- [Commits](https://github.com/sparklemotion/nokogiri/compare/v1.13.3...v1.13.4

)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: indirect
...

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

docs/Gemfile.lock

@@ -227,7 +227,7 @@ GEM
       jekyll-seo-tag (~> 2.1)
     minitest (5.14.4)
     multipart-post (2.1.1)
-    nokogiri (1.13.3-x86_64-linux)
+    nokogiri (1.13.4-x86_64-linux)
       racc (~> 1.4)
     nokogumbo (2.0.5)
       nokogiri (~> 1.8, >= 1.8.4)