Wrap websocket instantiation in try/catch to catch IE security errors

[mtharrison]

IE10/11 will throw a SecurityError when calling new Websocket(url), where url is considered to be an intranet site.

In this situation polling would still with s.io work but it doesn't have a chance because the SecurityError isn't being caught. I propose to wrap https://github.com/Automattic/socket.io-client/blob/master/socket.io.js#L3413 in a try/catch and emit an error on the transport if there is one, causing the transport to be frozen. Polling can then continue:

try {
    this.ws = new WebSocket(uri, protocols, opts);
} catch (e) {
    return this.emit('error', e);
}

[darrachequesne]

Closed by socketio/engine.io-client#475. Thanks for the report.