Change to official repo

[yubiuser]

Unfortunately the current repo used by the script (https://github.com/FossoresLP/vyatta-wireguard) is not maintained any longer in favor of the offcially wireguard repo at https://github.com/WireGuard/wireguard-vyatta-ubnt/releases.

Please change the download path accordingly.

P.S. Hope this is the last repo change in a while now... chances might be good, as Jason (zx2c4) is also contributing to this new repo.

[yubiuser]

Thanks.