Upgrade the gem to the latest format used by Rails

[mconf-daileon]

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Author Name: Leonardo Daronco (Leonardo Daronco)
Original Redmine Issue: 1809, http://dev.mconf.org/redmine/issues/1809

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The gem works with newer versions of Rails, but it is still using an old format from Rails 3.
There might be a few things that can be improved by updating the gem, such as the way the gem is plugged into the application. See http://guides.rubyonrails.org/engines.html