feat(Button): add htmlType prop for form submit button

[Kimi-Gao]

First of all, thank you for your contribution! :-)

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• Make sure that you propose PR to right branch: bugfix for master, feature for latest active branch feature-x.x.
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Extra checklist:

elif isNewFeature :

• Update API docs for the component.
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[codecov]

Codecov Report

Merging #278 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #278   +/-   ##
=======================================
  Coverage   17.86%   17.86%           
=======================================
  Files          71       71           
  Lines        1399     1399           
  Branches      314      314           
=======================================
  Hits          250      250           
  Misses        882      882           
  Partials      267      267           

Impacted Files	Coverage Δ
src/components/Button/index.js	100.00% <ø> (ø)

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