Update Engine.php

Add ```clear``` to the halt method in order to work as expected with the latest changes

flight/Engine.php

@@ -364,6 +364,7 @@ class Engine {
      */
     public function _halt($code = 200, $message = '') {
         $this->response()
+            ->clear()
             ->status($code)
             ->write($message)
             ->send();