add --domain option to enable localtunnel servers on subdomains

bin/server

@@ -24,6 +24,9 @@ const argv = optimist
         default: '0.0.0.0',
         describe: 'IP address to bind to'
     })
+    .options('domain', {
+        describe: 'Specify the base domain name. This is optional if hosting localtunnel from a regular example.com domain. This is required if hosting a localtunnel server from a subdomain (i.e. lt.example.dom where clients will be client-app.lt.example.come)',
+    })
     .options('max-sockets', {
         default: 10,
         describe: 'maximum number of tcp sockets each client is allowed to establish at one time (the tunnels)'
@@ -37,7 +40,8 @@ if (argv.help) {
 
 const server = CreateServer({
     max_tcp_sockets: argv['max-sockets'],
-    secure: argv.secure
+    secure: argv.secure,
+    domain: argv.domain,
 });
 
 server.listen(argv.port, argv.address, () => {