Bump html-proofer from 3.18.5 to 3.18.6 (#198)

Bumps [html-proofer](https://github.com/gjtorikian/html-proofer) from 3.18.5 to 3.18.6.
- [Release notes](https://github.com/gjtorikian/html-proofer/releases)
- [Commits](gjtorikian/html-proofer@v3.18.5...v3.18.6)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile

@@ -1,7 +1,7 @@
 source 'https://rubygems.org'
 
 group :development, :test do
-  gem 'html-proofer', '~> 3.18.5'
+  gem 'html-proofer', '~> 3.18.6'
   gem 'jekyll', '~> 4.2.0'
   gem 'jekyll-feed', '~> 0.15.1'
   gem 'jekyll-paginate', '~> 1.1.0'

Gemfile.lock

@@ -18,7 +18,7 @@ GEM
     ffi-win32-extensions (1.0.4)
       ffi
     forwardable-extended (2.6.0)
-    html-proofer (3.18.5)
+    html-proofer (3.18.6)
       addressable (~> 2.3)
       mercenary (~> 0.3)
       nokogumbo (~> 2.0)
@@ -123,7 +123,7 @@ PLATFORMS
   x64-mingw32
 
 DEPENDENCIES
-  html-proofer (~> 3.18.5)
+  html-proofer (~> 3.18.6)
   jekyll (~> 4.2.0)
   jekyll-feed (~> 0.15.1)
   jekyll-paginate (~> 1.1.0)