Bump nokogiri from 1.13.4 to 1.15.4 in /docs

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.13.4 to 1.15.4.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.13.4...v1.15.4)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: direct:production
...

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

docs/Gemfile

@@ -3,6 +3,6 @@ source "https://rubygems.org"
 gem 'github-pages', group: :jekyll_plugins
 
 # Added at 2019-11-25 10:11:40 -0800 by jhoward:
-gem "nokogiri", "< 1.13.5"
+gem "nokogiri", "< 1.15.5"
 gem "jekyll", ">= 3.7"
 gem "kramdown", ">= 2.3.0"

docs/Gemfile.lock

@@ -201,23 +201,23 @@ GEM
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.3.6)
-    mini_portile2 (2.8.0)
+    mini_portile2 (2.8.4)
     minima (2.5.1)
       jekyll (>= 3.5, < 5.0)
       jekyll-feed (~> 0.9)
       jekyll-seo-tag (~> 2.1)
     minitest (5.14.1)
     multipart-post (2.1.1)
-    nokogiri (1.13.4)
-      mini_portile2 (~> 2.8.0)
+    nokogiri (1.15.4)
+      mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
     octokit (4.18.0)
       faraday (>= 0.9)
       sawyer (~> 0.8.0, >= 0.5.3)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
     public_suffix (3.1.1)
-    racc (1.6.0)
+    racc (1.7.1)
     rb-fsevent (0.10.4)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
@@ -257,7 +257,7 @@ DEPENDENCIES
   github-pages
   jekyll (>= 3.7)
   kramdown (>= 2.3.0)
-  nokogiri (< 1.13.5)
+  nokogiri (< 1.15.5)
 
 BUNDLED WITH
    2.0.2