add alias for moretrees:slab_acacia_planks, fixes #4

mods/stairs/init.lua

@@ -12,6 +12,9 @@ stairs = {}
 minetest.register_alias("stairs:stair_pinewood", "stairs:stair_pine_wood")
 minetest.register_alias("stairs:slab_pinewood", "stairs:slab_pine_wood")
 
+-- https://git.tchncs.de/Illuna-Minetest/illuna/issues/4
+
+minetest.register_alias("moretrees:slab_acacia_planks", "stairs:slab_acacia_wood")   
 
 -- Get setting for replace ABM