xcode7 + iOS10 程序在前台为什么接收不到消息，在后台可以接收到。
在前台没有任何打印，不调用这2个方法
- (void)application:(UIApplication *)application
didReceiveRemoteNotification:(NSDictionary *)userInfo{
}
- (void)application:(UIApplication *)application
didReceiveRemoteNotification:(NSDictionary *)userInfo
fetchCompletionHandler:
(void (^)(UIBackgroundFetchResult))completionHandler {
}