Bump html-proofer from 3.14.1 to 3.18.8

Bumps [html-proofer](https://github.com/gjtorikian/html-proofer) from 3.14.1 to 3.18.8.
- [Release notes](https://github.com/gjtorikian/html-proofer/releases)
- [Commits](gjtorikian/html-proofer@v3.14.1...v3.18.8)

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

Author: dependabot[bot]

Gemfile.lock

@@ -87,10 +87,10 @@ GEM
     html-pipeline (2.14.0)
       activesupport (>= 2)
       nokogiri (>= 1.4)
-    html-proofer (3.14.1)
+    html-proofer (3.18.8)
       addressable (~> 2.3)
       mercenary (~> 0.3)
-      nokogiri (~> 1.10)
+      nokogumbo (~> 2.0)
       parallel (~> 1.3)
       rainbow (~> 3.0)
       typhoeus (~> 1.3)
@@ -223,10 +223,12 @@ GEM
     nokogiri (1.11.2)
       mini_portile2 (~> 2.5.0)
       racc (~> 1.4)
+    nokogumbo (2.0.5)
+      nokogiri (~> 1.8, >= 1.8.4)
     octokit (4.20.0)
       faraday (>= 0.9)
       sawyer (~> 0.8.0, >= 0.5.3)
-    parallel (1.19.0)
+    parallel (1.20.1)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
     public_suffix (4.0.6)
@@ -263,7 +265,7 @@ GEM
       unf_ext
     unf_ext (0.0.7.7)
     unicode-display_width (1.7.0)
-    yell (2.2.0)
+    yell (2.2.2)
     zeitwerk (2.4.2)
 
 PLATFORMS