fix hotstone groups so it's possible to dig it again

nodes.lua

@@ -95,7 +95,7 @@ minetest.register_node("illuna:hotstone", {
     description = "Hot Stone",
     paramtype2 = "facedir",
     tiles = {"illuna_hotstone.png"},
-    groups = {choppy=2, igniter = 1},
+    groups = {cracky = 2, igniter = 1, stone = 1},
     light_source = 4,
     damage_per_second = 6,
     sounds = default.node_sound_stone_defaults(),