Fix routing TCP upgrades via express middleware

Currently, if there was a POST request with 'tcp' upgrade, the code just hangs and waits
till timeout.

Instead, let express code will give us a default 'finalhandler' which responds
appropriately - https://github.com/expressjs/express/blob/master/lib/application.js#L161

https://github.com/pillarjs/finalhandler/blob/master/index.js#L57 for future reference
on how to call this callback should socket.destroy need to be called.

src/server.js

@@ -218,13 +218,9 @@ function initializeExpressSync() {
                          '\r\n');
         };
 
-        // route through express middleware
-        app(req, res, function (error) {
-            if (error) {
-                console.error(error);
-                socket.destroy();
-            }
-        });
+        // route through express middleware. if we provide no callback, express will provide a 'finalhandler'
+        // TODO: it's not clear if socket needs to be destroyed
+        app(req, res);
     });
 
     return httpServer;