Reset highlightedIndex to defaultHighlightIndex after selecting item

[SpaceK33z]

What:
Fixes #194

Why:

As a user I'd expect highlightedIndex to always have the value that I initially set it to, after selecting an item. I.e. react-select also works like this. It allows the user to quickly hit enter when the right item is the first in the list.

How:

highlightedIndex was always set to null when selecting an item. I changed that to be set to the defaultHighlightedIndexprop.

Checklist:

• Documentation N/A
• Tests
• Ready to be merged
• Added myself to contributors table

[codecov-io]

Codecov Report

Merging #195 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #195   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           4      4           
  Lines         267    267           
  Branches       61     61           
=====================================
  Hits          267    267

Impacted Files	Coverage Δ
src/downshift.js	100% <ø> (ø)	⬆️

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[kentcdodds]

Looks perfect! Thanks!

[kentcdodds]

Would you like to add yourself to the contributors table?