pantheon.updateScript: always use github api
pantheon.updateScript: always use github api

Unfortunately elementary has suddenly decided to add ${version}-debian
tags into the mix which ls-remote will always sort last. I believe these tags
point to the deb-packaging branches in the repo's which we certainly
don't ever want to use as they contain no source.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs