Add return tag on initialize method in Item class

Author: iamlucianojr

src/Omnipay/Common/Item.php

@@ -35,6 +35,7 @@ public function __construct($parameters = null)
      * Initialize this item with the specified parameters
      *
      * @param array|null $parameters An array of parameters to set on this object
+     * @return $this Item
      */
     public function initialize($parameters = null)
     {