Lava cooling: Increase interval to 2

An excessive load has been reported caused by the node searching, so even
when no lava is present.

mods/default/functions.lua

@@ -136,7 +136,7 @@ if minetest.settings:get_bool("enable_lavacooling") ~= false then
 		label = "Lava cooling",
 		nodenames = {"default:lava_source", "default:lava_flowing"},
 		neighbors = {"group:cools_lava", "group:water"},
-		interval = 1,
+		interval = 2,
 		chance = 2,
 		catch_up = false,
 		action = function(...)