Add err into next fuction

When use connect-timeout plugins, the router will execute twice.

Server: 
```javascript
var express = require('express');
var timeout = require('connect-timeout');
var app = express();
var expressWs = require('express-ws');
var http = require('http');

function main(cb) {

    app.use(timeout('5s'));

    app.use(haltOnTimedout);

    var server = http.createServer(app);

    expressWs(app, server);
    // Listen on http port.
    server.listen(app.get('port'), function () {
        cb(server, app);
    });

}

function haltOnTimedout(req, res, next) {
    if (!req.timedout) next();
}

app.ws('/echo', function(ws, req){
  // 5s later, this will execute once again
  console.log('execute twice');
});

main(function(){
  console.log('start');
});

```