Fix deprecated Relation#all in Rails 4, use Relation#to_a instead

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`). (called from followers at .../socialization/lib/socialization/stores/active_record/follow.rb:69)
Drop support for 1.9.2
Merge pull request #26 from thomas88/fix-relation-all-deprecation

Relation#all is deprecated in Rails 4, use Relation#to_a instead