Deprecated warning for .all

DEPRECATION WARNING: Relation#all is deprecated. If you want to eager-load a relation, you can call #load (e.g. `Post.where(published: true).load`). If you want to get an array of records from a relation, you can call #to_a (e.g. `Post.where(published: true).to_a`). 

By changing the self.to_a we solve the deprecation warning in rails 4.
Merge pull request #19 from Rongorongo/patch-1

Deprecated warning for .all