Fix useKeyboard example

[spbyrne]

In the useKeyboard doc it has an example using both the onKeyDown and onKeyUp handlers, but both were actually using onKeyDown. I've changed the second handler to onKeyUp since it seems that was intended.

  let {keyboardProps} = useKeyboard({
    onKeyDown: e => setEvents(
      events => [`key down: ${e.key}`, ...events]
    ),
    onKeyUp: e => setEvents(
      events => [`key up: ${e.key}`, ...events]
    )
  });

[devongovett]

Thank you!