Bump nokogiri from 1.6.8 to 1.13.4

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.6.8 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@v1.6.8...v1.13.4)

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

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

Author: dependabot[bot]

Gemfile.lock

@@ -18,6 +18,7 @@ GEM
     execjs (2.7.0)
     faraday (0.9.2)
       multipart-post (>= 1.2, < 3)
+    ffi (1.9.14)
     ffi (1.9.14-x64-mingw32)
     gemoji (2.1.0)
     github-pages (89)
@@ -93,17 +94,19 @@ GEM
       rb-fsevent (>= 0.9.3)
       rb-inotify (>= 0.9.7)
     mercenary (0.3.6)
-    mini_portile2 (2.1.0)
+    mini_portile2 (2.8.0)
     minitest (5.9.0)
     multipart-post (2.0.0)
     net-dns (0.8.0)
-    nokogiri (1.6.8-x64-mingw32)
-      mini_portile2 (~> 2.1.0)
-      pkg-config (~> 1.1.7)
+    nokogiri (1.13.4)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
+    nokogiri (1.13.4-x64-mingw32)
+      racc (~> 1.4)
     octokit (4.3.0)
       sawyer (~> 0.7.0, >= 0.5.3)
-    pkg-config (1.1.7)
     public_suffix (1.5.3)
+    racc (1.6.0)
     rb-fsevent (0.9.7)
     rb-inotify (0.9.7)
       ffi (>= 0.5.0)
@@ -121,6 +124,7 @@ GEM
       thread_safe (~> 0.1)
 
 PLATFORMS
+  ruby
   x64-mingw32
 
 DEPENDENCIES