Allows bootstrapping win64 from win32 snapshot.
Remove triple = 'i686-pc-mingw32' once win64 snapshot is made.

Signed-off-by: Peter Atashian <retep998@gmail.com>
Merge commit '314d47749a79d0382eea1b710456b038a1ac84c0' into win64
Switch the URL from which nightlies are downloaded
auto merge of #562 : alexcrichton/cargo/win64, r=alexcrichton