Update IterableAPI.m (#62)

Author: davidtruong

Iterable-iOS-SDK/IterableAPI.m

@@ -1186,7 +1186,7 @@ - (void)spawnInAppNotification:(ITEActionBlock)callbackBlock
 
                     IterableNotificationMetadata *notification = [IterableNotificationMetadata metadataFromInAppOptions:messageId];
 
-                    dispatch_sync(dispatch_get_main_queue(), ^{
+                    dispatch_async(dispatch_get_main_queue(), ^{
                         [IterableInAppManager showIterableNotificationHTML:html trackParams:(IterableNotificationMetadata*)notification callbackBlock:(ITEActionBlock)callbackBlock backgroundAlpha:backgroundAlpha padding:edgeInsets];
                     });
                 } else {