Fix Windows nightly links.

The homepage was linking to outdated nightlies. This had been fixed in the readme, but not on the actual website.
auto merge of #891 : ruud-v-a/cargo/patch-1, r=alexcrichton

The homepage was linking to outdated nightlies. This had been fixed in the readme, but not on the actual website.
Merge remote-tracking branch 'upstream/master'