Bump nokogiri from 1.10.9 to 1.13.4 in /site/jekyll

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] <support@github.com>

Author: dependabot[bot]

site/jekyll/Gemfile.lock

@@ -39,12 +39,13 @@ GEM
       rb-inotify (>= 0.9)
       rb-kqueue (>= 0.2)
     maruku (0.7.0)
-    mini_portile2 (2.4.0)
+    mini_portile2 (2.8.0)
     multi_json (1.12.1)
-    nokogiri (1.10.9)
-      mini_portile2 (~> 2.4.0)
-    nokogiri (1.10.9-x64-mingw32)
-      mini_portile2 (~> 2.4.0)
+    nokogiri (1.13.4)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
+    nokogiri (1.13.4-x64-mingw32)
+      racc (~> 1.4)
     nokogumbo (2.0.2)
       nokogiri (~> 1.8, >= 1.8.4)
     parslet (1.5.0)
@@ -53,6 +54,7 @@ GEM
     pygments.rb (0.5.4)
       posix-spawn (~> 0.3.6)
       yajl-ruby (~> 1.1.0)
+    racc (1.6.0)
     rack (1.6.12)
     rb-fsevent (0.9.8)
     rb-inotify (0.9.8)