use set_node(), not add_node()

don't use minetest.env:* method (deprecated), use minetest.* instead

dryplants/moregrass.lua

@@ -13,7 +13,7 @@ abstract_dryplants.grow_grass = function(pos)
 	local grass_size = math.random(1,5)
 	if minetest.get_node(right_here).name == "air"  -- instead of check_air = true,
 	or minetest.get_node(right_here).name == "default:junglegrass" then
-		minetest.add_node(right_here, {name="default:grass_"..grass_size})
+		minetest.set_node(right_here, {name="default:grass_"..grass_size})
 	end
 end