Android Service startForeground不显示Notification的办法

参考地址:
http://blog.youkuaiyun.com/warren288/article/details/51104214

Failed to post notification on channel “null”消息栏无法显示
解决方式:
http://blog.youkuaiyun.com/Yooolanda/article/details/77857950
https://stackoverflow.com/questions/45668079/notificationchannel-issue-in-android-o

android O 要求:
if (Build.VERSION.SDK_INT > Build.VERSION_CODES.N_MR1) {
mContext.startForegroundService(myIntent);
} else {
mContext.startService(myIntent);
}