discord: make update script work for all branches

pkgs/applications/networking/instant-messengers/discord/darwin.nix

···
-{ pname, version, src, openasar, meta, stdenv, binaryName, desktopName, lib, undmg, makeWrapper, withOpenASAR ? false }:
+{ pname, version, src, openasar, meta, stdenv, binaryName, desktopName, lib, undmg, makeWrapper, branch, withOpenASAR ? false }:
 
 stdenv.mkDerivation {
   inherit pname version src meta;

pkgs/applications/networking/instant-messengers/discord/default.nix

···
       (_: value:
         callPackage package (value
           // {
-          inherit src version openasar;
+          inherit src version openasar branch;
           meta = meta // { mainProgram = value.binaryName; };
         }))
       {

pkgs/applications/networking/instant-messengers/discord/linux.nix

···
 , libXScrnSaver, libXcomposite, libXcursor, libXdamage, libXext, libXfixes
 , libXi, libXrandr, libXrender, libXtst, libxcb, libxshmfence, mesa, nspr, nss
 , pango, systemd, libappindicator-gtk3, libdbusmenu, writeScript, python3, runCommand
+, branch
 , common-updater-scripts, withOpenASAR ? false }:
 
 let
···
       }?platform=linux&format=tar.gz" | grep -oP 'location: \K\S+')
       version=''${url##https://dl*.discordapp.net/apps/linux/}
       version=''${version%%/*.tar.gz}
-      update-source-version ${pname} "$version" --file=./pkgs/applications/networking/instant-messengers/discord/default.nix
+      update-source-version ${pname} "$version" --file=./pkgs/applications/networking/instant-messengers/discord/default.nix --version-key=${branch}
     '';
   };
 }