Bump nokogiri from 1.6.2.1 to 1.6.8.1

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.6.2.1 to 1.6.8.1.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.6.2.1...v1.6.8.1)

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

Author: dependabot[bot]

Gemfile.lock

@@ -112,12 +112,12 @@ GEM
       treetop (~> 1.4.8)
     method_source (0.8.2)
     mime-types (1.25.1)
-    mini_portile (0.6.0)
+    mini_portile2 (2.1.0)
     minitest (4.7.5)
     multi_json (1.10.1)
     multi_test (0.1.1)
-    nokogiri (1.6.2.1)
-      mini_portile (= 0.6.0)
+    nokogiri (1.6.8.1)
+      mini_portile2 (~> 2.1.0)
     pg (0.15.1)
     polyglot (0.3.5)
     pry (0.10.0)