Bump nokogiri from 1.8.1 to 1.13.6

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.8.1 to 1.13.6.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](https://github.com/sparklemotion/nokogiri/compare/v1.8.1...v1.13.6)

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

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

Gemfile.lock

@@ -51,12 +51,13 @@ GEM
       ruby_dep (~> 1.2)
     method_source (0.9.0)
     mini_mime (0.1.4)
-    mini_portile2 (2.3.0)
+    mini_portile2 (2.8.0)
     minitest (5.10.3)
     multi_json (1.12.2)
     mustermann (1.0.1)
-    nokogiri (1.8.1)
-      mini_portile2 (~> 2.3.0)
+    nokogiri (1.13.6)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
     poltergeist (1.16.0)
       capybara (~> 2.1)
       cliver (~> 0.3.1)
@@ -65,6 +66,7 @@ GEM
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
     public_suffix (3.0.0)
+    racc (1.6.0)
     rack (2.0.3)
     rack-protection (2.0.0)
       rack