Issue #3 back-port for Omnipay 2.x

Author: judgej

src/Traits/HasCompleteResponse.php

@@ -107,6 +107,16 @@ public function isSuccessful()
         return $status === Gateway::STATUS_SUCCESS || $status === Gateway::STATUS_ACCEPTED;
     }
 
+    /**
+     * @return bool
+     */
+    public function isCancelled()
+    {
+        $status = $this->getStatus();
+
+        return $status === Gateway::STATUS_CANCEL;
+    }
+
     /**
      * CHECKME: is the virtualCardno the same thing, but for specific payment methods?
      *