Merge pull request #2006 from progit/dependabot/bundler/epubcheck-ruby-5.2.0.0

Update epubcheck-ruby requirement from 5.1.0.0 to 5.2.0.0

Author: ben

Gemfile

@@ -13,6 +13,6 @@ gem 'asciidoctor-pdf', '2.3.17'
 gem 'coderay', '1.1.3'
 gem 'pygments.rb', '2.4.1'
 gem 'thread_safe', '0.3.6'
-gem 'epubcheck-ruby', '5.1.0.0'
+gem 'epubcheck-ruby', '5.2.0.0'
 gem 'html-proofer', '5.0.9'
 gem 'kindlegen', '3.1.1'