Using socket.io in Cloud9 always get the xhr-polling transportation method-open source projects ajaxorg/cloud9

I’m developing an app that uses socket.io, but it always fallback to xhr polling transportation method, and I can’t understand why.

I’m using Chrome, but I already tested with other browsers, and the xhr polling transportation method still be used.

I’m using Cloud9 IDE in c9.io.

Have you ever saw this behaviour?