Move AR include into engine file.

app/models/impressionist/impressionable.rb

@@ -69,5 +69,3 @@ module Impressionist
 
   end
 end
-
-ActiveRecord::Base.send(:include, Impressionist::Impressionable)

lib/impressionist/engine.rb

@@ -4,7 +4,7 @@ require "rails"
 module Impressionist
   class Engine < Rails::Engine
     initializer 'impressionist.extend_ar' do |app|
-      ActiveRecord::Base.extend Impressionist::Impressionable
+      ActiveRecord::Base.send(:include, Impressionist::Impressionable)
     end
 
     initializer 'impressionist.controller' do