Bump nokogiri from 1.11.4 to 1.13.4 in /example_app

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.11.4 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](sparklemotion/nokogiri@v1.11.4...v1.13.4)

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

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

Author: dependabot[bot]

example_app/Gemfile.lock

@@ -40,23 +40,23 @@ GEM
     metaclass (0.0.4)
     method_source (0.9.0)
     mini_mime (0.1.4)
-    mini_portile2 (2.5.1)
+    mini_portile2 (2.8.0)
     minitest (5.10.3)
     mocha (1.3.0)
       metaclass (~> 0.0.1)
     multipart-post (2.1.1)
     mustermann (1.1.1)
       ruby2_keywords (~> 0.0.1)
-    nokogiri (1.11.4)
-      mini_portile2 (~> 2.5.0)
+    nokogiri (1.13.4)
+      mini_portile2 (~> 2.8.0)
       racc (~> 1.4)
     octokit (4.7.0)
       sawyer (~> 0.8.0, >= 0.5.3)
     pry (0.11.1)
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
     public_suffix (4.0.6)
-    racc (1.5.2)
+    racc (1.6.0)
     rack (2.2.3)
     rack-flash3 (1.0.5)
       rack