[Security] Bump nokogiri from 1.10.4 to 1.10.6 (#1122)

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.10.4 to 1.10.6. **This update includes a security fix.**
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.10.4...v1.10.6)

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

Gemfile.lock

@@ -164,7 +164,7 @@ GEM
     mysql2 (0.5.2)
     net-http-persistent (2.9.4)
     nio4r (2.5.2)
-    nokogiri (1.10.4)
+    nokogiri (1.10.6)
       mini_portile2 (~> 2.4.0)
     oa-core (0.3.2)
     oa-openid (0.3.2)