Fix cursor position updates in downshift's combobox input

[alostsock]

Making this as a note to myself. This only happens on mobile as far as I can tell -- there's probably some kind of race condition, or at least some conflict in state management happening.

Some hints of what is going on here:
downshift-js/downshift#1108 (comment)
and one of the mentioning issues:
twilio-labs/paste#2647

Haven't looked into it to see what the "proper" fix is yet.

[alostsock]

Seems to be fixed with 6c56965

[alostsock]

The previous commit fixed the issue, but doesn't populate the default values from cache anymore, so I've reverted it for now. Probably need to go with the solution in the linked downshift issue, to basically make the input fully controlled.

EDIT: Ah, nevermind. This was actually broken by #8

[alostsock]

Should be fixed by 2a187e0, I think state wasn't being populated by mobx properly.