Move the private property definition to the top of the class

lib/API/JSON/v1/MP2Migrator.php

@@ -11,13 +11,12 @@ class MP2Migrator extends APIEndpoint {
   public $permissions = array(
     'global' => AccessControl::PERMISSION_MANAGE_SETTINGS
   );
+  private $MP2Migrator;
 
   public function __construct() {
     $this->MP2Migrator = new \MailPoet\Config\MP2Migrator();
   }
 
-  private $MP2Migrator;
-
   /**
    * Import end point
    *