dante service: fix config option type

The type was simply str but the default is null, thus resulting in a
conversion error if the user fails to declare a value.

Changed files
+1 -1
nixos
modules
services
networking
+1 -1
nixos/modules/services/networking/dante.nix
···
config = mkOption {
default = null;
-
type = types.str;
+
type = types.nullOr types.str;
description = ''
Contents of Dante's configuration file
NOTE: user.privileged/user.unprivileged are set by the service