Replaces base url with curl

[cauldnz]

Appears that Weather Underground may have their knickers in a knot over page scraping?

Replaced the base url function with curl. I think that curl probably does a better job of spoofing the request headers. Thus, knickers un-knotted and weather data flowing again.

Have tested and "works on my machine"... but I will admit this is my first pull-request :-)

[Ram-N]

Chris, CI checks are failing. I don't know if it doesn't like rCurl, or if something else is going on. Can someone paste the error they are receiving? That would help us debug the issue.

[ozagordi]

What about adding curl into requirements listed in DESCRIPTION?