nixos/minetest-server: Fix port coercion

Fix coercion of minetest-server port.

Changed files
+1 -1
nixos
modules
services
+1 -1
nixos/modules/services/games/minetest-server.nix
···
let
cfg = config.services.minetest-server;
-
flag = val: name: if val != null then "--${name} ${val} " else "";
+
flag = val: name: if val != null then "--${name} ${toString val} " else "";
flags = [
(flag cfg.gameId "gameid")
(flag cfg.world "world")