fix notification service startForeground issue
sometimes the app crashes in android 8.x because it takes too long to call startForeground(int notificationId, Notification notification) after the openvpn service was started with context.startForegroundService(startVPN);
it is a well known android issue on android O but we should find a work around to minimize the chance this exception can get thrown.
FATAL EXCEPTION: main
Process: se.leap.bitmaskclient, PID: 17975
android.app.RemoteServiceException: Bad notification for startForeground: java.lang.RuntimeException: invalid channel for service notification: Notification(channel=bitmask_void_vpn_news pri=2 contentView=null vibrate=null sound=null tick defaults=0x0 flags=0x14a color=0x00000000 category=service actions=1 vis=PRIVATE)