use | to have more intent revealing code

thanks to @egilburg for suggestion

Author: Neeraj Singh

activerecord/lib/active_record/associations/association_scope.rb

@@ -101,7 +101,7 @@ def add_constraints(scope)
 
             scope.includes! item.includes_values
             scope.where_values += item.where_values
-            scope.order_values += (item.order_values - scope.order_values)
+            scope.order_values |= item.order_values
           end
         end