fix deprecated mingetty option

Author: Mic92

share/nixos-shell/nixos-shell.nix

@@ -96,12 +96,16 @@ in {
       # Allow the user to login as root without password.
       users.extraUsers.root.initialHashedPassword = "";
 
-      services.getty.helpLine = ''
-        Log in as "root" with an empty password.
-        If you are connect via serial console:
-        Type Ctrl-a c to switch to the qemu console
-        and `quit` to stop the VM.
-      '';
+      services = let
+        service = if lib.versionAtLeast (lib.versions.majorMinor lib.version) "20.09" then "getty" else "mingetty";
+      in {
+        ${service}.helpLine = ''
+          Log in as "root" with an empty password.
+          If you are connect via serial console:
+          Type Ctrl-a c to switch to the qemu console
+          and `quit` to stop the VM.
+        '';
+      };
 
       virtualisation = {
         graphics = mkVMDefault false;