Pass the metrics address fd to the child process

Closes #44 (closed)

daemon.go

@@ -205,6 +205,7 @@ func daemonize(config appConfig, uid, gid uint) {
 	daemonUpdateFds(cmd, config.ListenHTTP)
 	daemonUpdateFds(cmd, config.ListenHTTPS)
 	daemonUpdateFds(cmd, config.ListenProxy)
+	config.ListenMetrics = daemonUpdateFd(cmd, config.ListenMetrics)
 	// Start the process
 	if err = cmd.Start(); err != nil {