Fix for skybox.add function not working. (#8)

When using the skybox.add function, worlds fail to load with the following error:
/skybox/init.lua:90: attempt to call field 'add' (a nil value)

Using table.insert instead allows this to work without any added dependencies.

init.lua

@@ -90,7 +90,7 @@ skybox.clear = function(player)
 end
 
 skybox.add = function(def)
-	table.add(skies, def)
+	table.insert(skies, def)
 end
 
 skybox.get_skies = function()