Support for TypeScript 3.x

[andreifloricel]

I'm trying to integrate the library in a project which still has to support TypeScript 3.8.x
I can't do that due to a single breaking change from TS v4.x: the labeled tupled elements in FocusContextValue
https://github.com/gpbl/react-day-picker/blob/v8.0.0-beta.29/packages/react-day-picker/src/contexts/FocusContext/FocusContextValue.ts

Would it be possible to adjust the typings in order to be backwards compatible with v3.x?
Thanks