localhost is hardocded

[maxday]

Hi !
I've notived that localhost is hardcoded
let datadog = options.dogstatsd || new hotShots.StatsD("localhost", 8125);

I can use the options.dogstatsd to create myself a new object with correct value but it may be easier for developpers to config host and port directly.

I've just pushed a PR which does it.
This is backward-compatible.