nixos/grafana-image-renderer: typo fix

Since the service doesn't do a strict config check, this worked fine
before, however the settings in the block never applied properly.

Changed files
+1 -1
nixos
modules
services
+1 -1
nixos/modules/services/monitoring/grafana-image-renderer.nix
···
timezone = config.time.timeZone;
};
-
services = {
+
service = {
logging.level = mkIf cfg.verbose (mkDefault "debug");
metrics.enabled = mkDefault false;
};