Remove observer on cleanup

atom/browser/mac/in_app_purchase_observer.mm

@@ -50,6 +50,14 @@ using InAppTransactionCallback =
   return self;
 }
 
+/**
+ * Cleanup.
+ */
+- (void)dealloc {
+  [[SKPaymentQueue defaultQueue] removeTransactionObserver:self];
+  [super dealloc];
+}
+
 /**
  * Run the callback in the browser thread.
  *