build: bump nokogiri from 1.10.3 to 1.10.4 in /docs

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.10.3 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/commits

)

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

docs/Gemfile.lock

@@ -214,7 +214,7 @@ GEM
       jekyll-seo-tag (~> 2.1)
     minitest (5.11.3)
     multipart-post (2.1.1)
-    nokogiri (1.10.3)
+    nokogiri (1.10.4)
       mini_portile2 (~> 2.4.0)
     octokit (4.14.0)
       sawyer (~> 0.8.0, >= 0.5.3)