Fix guid formatting in notifications

closes #262

Author: cpacia

market/contracts.py

@@ -693,7 +693,7 @@ def accept_receipt(self, notification_listener, blockchain, receipt_json=None):
             image_hash = unhexlify(self.contract["vendor_offer"]["listing"]["item"]["image_hashes"][0])
         else:
             image_hash = ""
-        buyer_guid = self.contract["buyer_order"]["order"]["id"]["guid"]
+        buyer_guid = unhexlify(self.contract["buyer_order"]["order"]["id"]["guid"])
         if "blockchain_id" in self.contract["buyer_order"]["order"]["id"]:
             handle = self.contract["buyer_order"]["order"]["id"]["blockchain_id"]
         else: