Added xboxleaders options to input url to constructor.

Hi,

We've been using your xboxleaders API for a couple of months and we're very happy with it.

We've now set up our own xboxleaders server, so and I've made a small change to node-uxla to allow a url option to be passed into the XboxLeaders constructor. 

Can you add this update to node-uxla and publish it to npm?

cheers,
Noel

p.s. I also made a small typo update!