nixos gdm: fix enable description

Changed files
+1 -1
nixos
modules
services
x11
display-managers
+1 -1
nixos/modules/services/x11/display-managers/gdm.nix
···
services.xserver.displayManager.gdm = {
enable = mkEnableOption ''
-
Whether to enable GDM as the display manager.
+
GDM as the display manager.
<emphasis>GDM is very experimental and may render system unusable.</emphasis>
'';