fix not use deprecated header (use correct with header)

README.md

@@ -178,6 +178,6 @@ If you do not want this, you can change this option but it is recommended to add
 ```PHP
 public function beforeRender(Event $event) {
     // ...
-    $this->response->withHeader('Access-Control-Allow-Origin', '*');
+    $this->response = $this->response->withHeader('Access-Control-Allow-Origin', '*');
 }
 ```

src/Controller/ErrorController.php

@@ -27,6 +27,6 @@ public function initialize()
     public function beforeRender(Event $event)
     {
         parent::beforeRender($event);
-        $this->response->header(['Access-Control-Allow-Origin' => '*']);
+        $this->response = $this->response->withHeader('Access-Control-Allow-Origin', '*');
     }
 }