Bump html-proofer from 3.18.6 to 3.18.7

Bumps [html-proofer](https://github.com/gjtorikian/html-proofer) from 3.18.6 to 3.18.7.
- [Release notes](https://github.com/gjtorikian/html-proofer/releases)
- [Commits](gjtorikian/html-proofer@v3.18.6...v3.18.7)

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

Gemfile.lock

@@ -87,7 +87,7 @@ GEM
     html-pipeline (2.14.0)
       activesupport (>= 2)
       nokogiri (>= 1.4)
-    html-proofer (3.18.6)
+    html-proofer (3.18.7)
       addressable (~> 2.3)
       mercenary (~> 0.3)
       nokogumbo (~> 2.0)