redshift-gammastep: migrate to lib.cli.toCommandLineShellGNU

Migrates from the deprecated toCommandLineShell to toCommandLineShellGNU.

This changes the output format from space-separated short options
(-c /path) to concatenated GNU-style options (-c/path). Both formats
were verified to work correctly with redshift and gammastep.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

modules/services/redshift-gammastep/lib/options.nix

@@ -239,7 +239,7 @@ in
             configFullPath = config.xdg.configHome + "/${xdgConfigFilePath}";
           in
           "${cfg.package}/bin/${command} "
-          + lib.cli.toGNUCommandLineShell { } {
+          + lib.cli.toCommandLineShellGNU { } {
             v = cfg.enableVerboseLogging;
             c = configFullPath;
           };