Merge pull request #1718 from progit/dependabot/bundler/html-proofer-3.19.3

Update html-proofer requirement from 3.19.2 to 3.19.3

Author: ben

Gemfile

@@ -13,5 +13,5 @@ gem 'coderay', '1.1.3'
 gem 'pygments.rb', '2.2.0'
 gem 'thread_safe', '0.3.6'
 gem 'epubcheck-ruby', '4.2.6.0'
-gem 'html-proofer', '3.19.2'
+gem 'html-proofer', '3.19.3'
 gem 'kindlegen', '3.1.1'