give_initial_stuff: syntax correction for default initial stuff

mods/give_initial_stuff/init.lua

 local stuff_string = minetest.settings:get("initial_stuff") or
-		"illuna:noobcoin 42" ..
-		"magical_potion:fly_small 2"
+		"illuna:noobcoin 42,magical_potion:fly_small 2"
 
 give_initial_stuff = {
 	items = {}