make fulfillment api as parent resource

Author: Jin

lib/ShopifySDK.php

@@ -85,6 +85,7 @@
  * @property-read DiscountCode $DiscountCode
  * @property-read DraftOrder $DraftOrder
  * @property-read Event $Event
+ * @property-read Fulfillment $Fulfillment
  * @property-read FulfillmentService $FulfillmentService
  * @property-read GiftCard $GiftCard
  * @property-read InventoryItem $InventoryItem
@@ -131,6 +132,7 @@
  * @method DraftOrder DraftOrder(integer $id = null)
  * @method DiscountCode DiscountCode(integer $id = null)
  * @method Event Event(integer $id = null)
+ * @method Fulfillment Fulfillment(integer $id = null)
  * @method FulfillmentService FulfillmentService(integer $id = null)
  * @method FulfillmentOrder FulfillmentOrder(integer $id = null)
  * @method GiftCard GiftCard(integer $id = null)
@@ -186,6 +188,7 @@ class ShopifySDK
         'DiscountCode',
         'DraftOrder',
         'Event',
+        'Fulfillment',
         'FulfillmentService',
         'FulfillmentOrder',
         'GiftCard',