Add ability to craft 4 dirts using 4 gravels

- Solves #215

minetestforfun_game/mods/default/crafting.lua

@@ -665,6 +665,12 @@ minetest.register_craft({
 	}
 })
 
+minetest.register_craft({
+	output = "default:dirt 4",
+	type = "shapeless",
+	recipe = {"default:gravel", "default:gravel", "default:gravel", "default:gravel"}
+})
+
 minetest.register_craft({
 	output = "default:gravel",
 	recipe = {