nixos/rogue: Set WorkingDirectory to /tmp

Otherwise we can get an ugly /rogue.scr in the root of the filesystem
hierarchy.

nixos/modules/services/misc/rogue.nix

@@ -52,6 +52,7 @@ in
             TTYPath = "/dev/${cfg.tty}";
             TTYReset = true;
             TTYVTDisallocate = true;
+            WorkingDirectory = "/tmp";
             Restart = "always";
           };
       };