[php] add missing follow

src/generators/genphp7.ml

@@ -281,7 +281,7 @@ let is_dynamic_type (target:Type.t) = match follow target with TDynamic _ -> tru
 (**
 	Check if `target` is `php.Ref`
 *)
-let is_ref (target:Type.t) = match target with TType ({ t_path = type_path }, _) -> type_path = ref_type_path | _ -> false
+let is_ref (target:Type.t) = match follow_without_type target with TType ({ t_path = type_path }, _) -> type_path = ref_type_path | _ -> false
 
 (**
 	Check if `field` is a `dynamic function`