As expected, Apple added some options to control which older versions of an app are offered to users of older iOS versions that aren’t supported with the current version of an app:
Previous versions of your apps are now available for re‑download by users who have already purchased them, allowing customers to use your apps with older devices which may no longer be supported by the current version of your app. If you do not wish to make these versions available, you can manage the availability of your apps‘ previous versions in the Rights and Pricing section of the Manage Your Apps module in iTunes Connect.