Fix new ActiveRecord::Relation instance presentation for Rails>=4

This problem is described in StackOverflow thread.
http://stackoverflow.com/questions/23290040/why-doesnt-awesome-print-work-on-some-rails-collection-objects and also issued in #159.

*Tl;dr*
The class of Relation object in Rails>=4 is like:
> Post.all.class 
=> ActiveRecord::Relation::ActiveRecord_Relation_Post

This is a clear patch to solve this problem.