A11y - Active descendant not set on input

[4lbertoC]

Hello there,

I'm testing a11y on v3.0.3 but screen readers do not recognise the choices.
I noticed that the fix is already on the develop branch but not on master, which as far as I understood is the current reference for tags.

It's just about setting the correct aria-activedescendant attribute on the input field when a choice is highlighted.

I'm sending you a PR.
Do you see any potential side effect or is it possible to merge it?

Thank you!

[jshjohnson]

See conversation here: #316