Applied keyword argument fixes on Ruby 2.2.0

Ruby 2.2.0 will change keyword arguments behavior. rails already fixed this changes. I found same code in bullet and fixed it. 

see also.
 * https://bugs.ruby-lang.org/issues/9593
 * https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/45272
 * https://github.com/rails/rails/blob/4-0-stable/activerecord/lib/active_record/associations/has_many_association.rb#L76