Fix hud_elem_type deprecation in areas mod

mods/tutorial_areas/hud.lua

@@ -6,6 +6,16 @@ else
   S = function ( s ) return s end
 end
 
+-- Legacy support: Name of the HUD type field for 'hud_add'.
+local hud_type_field_name
+if minetest.features.hud_def_type_field then
+	-- engine version 5.9.0 and later
+	hud_type_field_name = "type"
+else
+	-- All engine versions before 5.9.0
+	hud_type_field_name = "hud_elem_type"
+end
+
 areas.hud = {}
 
 minetest.register_globalstep(function(dtime)
@@ -24,7 +34,7 @@ minetest.register_globalstep(function(dtime)
 			hud = {}
 			areas.hud[name] = hud
 			hud.areasId = player:hud_add({
-				hud_elem_type = "text",
+				[hud_type_field_name] = "text",
 				name = "Areas",
 				number = 0xFFFFFF,
 				position = {x=1, y=0.25},