Add support for proxies

[bunnyhugdev]

I'm behind a proxy in my corporate setting and to get grunt-retire to work I had to modify tasks/retire.js to allow for a proxy (I just hardcoded mine into the request.get call). Would be nice if I could specify something like that in the task config.

[eoftedal]

@phun-ky Can you publish the new version, or better do a npm owner add eoftedal grunt-retire allowing me to publish myself?

[phun-ky]

Tried, but atm npmjs.org gives me socket hang up, and I can't even access the site. Will try continuously ;)