[fix] 修复 laravel < 5.7版本不支持 add方法的bug

Author: telanflow

src/DTO/FieldDTOCollection.php

@@ -16,7 +16,7 @@ public static function makeFromArray(array $fields): self
             } else {
                 $v = FieldDTO::makeFromObject($field);
             }
-            $collection->add($v);
+            $collection->push($v);
         }
         return $collection;
     }