Bump nokogiri from 1.10.9 to 1.13.4 in /example_app

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.10.9 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@v1.10.9...v1.13.4)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

example_app/Gemfile.lock

@@ -101,12 +101,13 @@ GEM
     method_source (0.9.2)
     mimemagic (0.3.3)
     mini_mime (1.0.2)
-    mini_portile2 (2.4.0)
+    mini_portile2 (2.8.0)
     minitest (5.12.2)
     msgpack (1.3.1)
     nio4r (2.5.2)
-    nokogiri (1.10.9)
-      mini_portile2 (~> 2.4.0)
+    nokogiri (1.13.4)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
     pg (1.1.4)
     prometheus-client (0.9.0)
       quantile (~> 0.2.1)
@@ -121,6 +122,7 @@ GEM
     puma (4.3.3)
       nio4r (~> 2.0)
     quantile (0.2.1)
+    racc (1.6.0)
     rack (2.0.8)
     rack-protection (2.0.7)
       rack