nixos/icewm: Update icewm start command

Preferred way to start session in icewm. [docs](https://ice-wm.org/man/icewm-session)

Author: kennycallado

nixos/modules/services/x11/window-managers/icewm.nix

@@ -17,7 +17,7 @@ in
       { name = "icewm";
         start =
           ''
-            ${pkgs.icewm}/bin/icewm &
+            ${pkgs.icewm}/bin/icewm-session &
             waitPID=$!
           '';
       };