URL formatter treats release/archive URLs as valid even though they're not supported

Though the url formatter support url like this:
https://github.com/rgrove/rawgit/archive/master.zip

but, both of these urls return 404 not found:
https://rawgit.com/rgrove/rawgit/archive/master.zip
https://cdn.rawgit.com/rgrove/rawgit/archive/master.zip

Is it possible to support release/archive tarball? It'll be very nice!

BTW, thanks for this cool service!
