add --domain option to enable localtunnel servers on subdomains

test/domain.js

@@ -0,0 +1,52 @@
+import http from 'http';
+import url from 'url';
+import assert from 'assert';
+import localtunnel from 'localtunnel';
+
+import CreateServer from '../server';
+
+const localtunnel_server = CreateServer({
+    domain: 'domain.example.com',
+});
+
+process.on('uncaughtException', (err) => {
+    console.error(err);
+});
+
+process.on('unhandledRejection', (reason, promise) => {
+    console.error(reason);
+});
+
+suite('domain');
+
+var lt_server_port;
+
+before('set up localtunnel server', function(done) {
+    var server = localtunnel_server.listen(function() {
+        lt_server_port = server.address().port;
+        done();
+    });
+});
+
+test('landing page', function(done) {
+    var opt = {
+        host: 'localhost',
+        port: lt_server_port,
+        headers: {
+            host: 'domain.example.com'
+        },
+        path: '/'
+    }
+
+    var req = http.request(opt, function(res) {
+        res.setEncoding('utf8');
+        assert.equal(res.headers.location, 'https://localtunnel.github.io/www/')
+        done();
+    });
+
+    req.end();
+});
+
+after('shutdown', function() {
+    localtunnel_server.close();
+});