making paperclip compatible not only with ActiveRecord ORM

This patch only avoid reference to `ActiveRecord::Base.logger` if `ActiveRecord` is not available

lib/paperclip.rb

@@ -128,7 +128,7 @@ module Paperclip
     end
 
     def logger #:nodoc:
-      ActiveRecord::Base.logger
+      defined?(ActiveRecord::Base) ? ActiveRecord::Base.logger : Rails.logger
     end
 
     def logging? #:nodoc: