Replace deprecated function calls

mods/stairs/init.lua

@@ -23,7 +23,7 @@ local function rotate_and_place(itemstack, placer, pointed_thing)
 	local param2 = 0
 
 	if placer then
-		local placer_pos = placer:getpos()
+		local placer_pos = placer:get_pos()
 		if placer_pos then
 			param2 = minetest.dir_to_facedir(vector.subtract(p1, placer_pos))
 		end