fix(datepicker): fire onChange callback when typed date is invalid

[arthurdenner]

What kind of change does this PR introduce?
Bug fix. Closes #334.

What is the current behavior?
When the user types an invalid date, but input is updated but the onChange callback isn't fired.

What is the new behavior?
The callback is properly fired.

Checklist:

• Documentation
• Tests
• Ready to be merged

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[codecov]

Codecov Report

Merging #336 into develop will increase coverage by 0.91%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #336      +/-   ##
===========================================
+ Coverage    87.78%   88.70%   +0.91%     
===========================================
  Files           15       16       +1     
  Lines          475      487      +12     
  Branches        94       97       +3     
===========================================
+ Hits           417      432      +15     
+ Misses          56       53       -3     
  Partials         2        2              

Impacted Files	Coverage Δ
src/__tests__/_utils.tsx	100.00% <100.00%> (ø)
src/index.tsx	92.26% <100.00%> (+1.59%)	⬆️

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[arthurdenner]

🎉 This PR is included in version 2.9.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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