My Bike Friday Haul-a-day cargo bike came with an Altus derailleur index shifting an 8-speed cassette, 11-34T. I want to upgrade to a 9-speed 11-34T cassette and 9-speed shifter to get closer spacing on some of the mid-range gears. Will the Altus work with 9-speed index shifting? Or do I need to swap out the derailleur also?