[hotfix] Undo world flag and added mod_data

I was getting a little too fancy with my cuts... now this should make a
truely working copy

luanti/Dockerfile

@@ -45,5 +45,5 @@ EXPOSE 30000
 # Expose for map server
 #EXPOSE 8080
 
-CMD ["./bin/server", "--world", "world"]
+CMD ["./bin/server", "--worldname", "world"]