nix: change from pkgs.system to stdenv.hostPlatform.system

modules/server/minecraft.nix

@@ -0,0 +1,25 @@
+{
+  flake.modules.nixos.minecraft-server =
+    { ... }:
+    {
+      services.minecraft-server = {
+        enable = true;
+        eula = true;
+        openFirewall = true; # Opens the port the server is running on (by default 25565 but in this case 43000)
+        declarative = true;
+        whitelist = {
+          # This is a mapping from Minecraft usernames to UUIDs. You can use https://mcuuid.net/ to get a Minecraft UUID for a username
+          Daholli = "9e206940-3dfc-4331-b781-b43a9905087a";
+        };
+        serverProperties = {
+          server-port = 43000;
+          difficulty = 3;
+          gamemode = 1;
+          max-players = 5;
+          motd = "NixOS Minecraft server!";
+          white-list = true;
+        };
+        jvmOpts = "-Xms2048M -Xmx4096M";
+      };
+    };
+}