[1.x] add pending purchase canceled event (#128)

Author: monurakkaya

src/DeveloperNotifications/SubscriptionNotification.php

@@ -8,7 +8,7 @@
  * SubscriptionNotification Class
  * Subscription notification
  * {@link https://developer.android.com/google/play/billing/integrate}
- * {@https://developer.android.com/google/play/billing/rtdn-reference#sub}.
+ * {@link https://developer.android.com/google/play/billing/rtdn-reference#sub}.
  */
 class SubscriptionNotification implements NotificationPayload
 {
@@ -25,6 +25,7 @@ class SubscriptionNotification implements NotificationPayload
     public const SUBSCRIPTION_PAUSE_SCHEDULE_CHANGED = 11;
     public const SUBSCRIPTION_REVOKED = 12;
     public const SUBSCRIPTION_EXPIRED = 13;
+    public const SUBSCRIPTION_PENDING_PURCHASE_CANCELED = 20;
 
     /**
      * @var string

tests/DeveloperNotifications/SubscriptionNotificationTest.php

@@ -22,6 +22,7 @@ class SubscriptionNotificationTest extends TestCase
         SubscriptionNotification::SUBSCRIPTION_PAUSE_SCHEDULE_CHANGED,
         SubscriptionNotification::SUBSCRIPTION_REVOKED,
         SubscriptionNotification::SUBSCRIPTION_EXPIRED,
+        SubscriptionNotification::SUBSCRIPTION_PENDING_PURCHASE_CANCELED,
     ];
 
     /**