How to enable socket.io logging for Express.io 1.1.13

gistfile1.js

var app = require('express.io')();
var log4js = require('log4js');
var logger = log4js.getLogger('io');

app.http().io();
app.listen(7076)

app.io.set('logger', logger);
app.io.set('log level', log4js.levels.TRACE);