github.com utilizes Rouge for syntax highlighting. This is good, but it even
uses Rouge with markups that lack Rouge support. For example if you make a file
readme.org:

#+BEGIN_SRC ruby
puts 'hello world'
#+END_SRC

github.com will correctly render the file with highlighting. What is confusing
is that the Org-Ruby Gem currently only supports Coderay or Pygments.rb:

https://github.com/wallyqs/org-ruby#current-status

So how is github.com using Org-Ruby with Rouge?