Update provider.py

There was this code snippet "HEAD = lambda *args, **kwargs: request(*args, method="POST", **kwargs)" that I thought wouldn't be logical, looking at the lines around it, because every variable repeats its name in the method parameter, except for the HEAD, which repeats POST.
Hope it helps you.
Merge pull request #30 from tobiasvandriessel/patch-1

Update provider.py