Add #to_hash conversion protocol to object serializer

Author: iamvery

lib/fast_jsonapi/object_serializer.rb

@@ -42,6 +42,7 @@ def serializable_hash
 
       hash_for_one_record
     end
+    alias_method :to_hash, :serializable_hash
 
     def hash_for_one_record
       serializable_hash = { data: nil }