item: populate missing return type information

src/pocketmine/item/Consumable.php

@@ -49,6 +49,8 @@ interface Consumable{
 	 * Called when this Consumable is consumed by mob, after standard resulting effects have been applied.
 	 *
 	 * @param Living $consumer
+	 *
+	 * @return void
 	 */
 	public function onConsume(Living $consumer);
 }