fix dnsmasq bug, fs.writeFile is not async-safe
fix dnsmasq bug, fs.writeFile is not async-safe

use fs.writeFileSync instead

firewalla/firewalla,MelvinTo/firewalla,MelvinTo/firewalla,MelvinTo/firewalla,MelvinTo/firewalla,firewalla/firewalla,firewalla/firewalla,firewalla/firewalla,firewalla/firewalla,MelvinTo/firewalla