SG & MY Postal validation

[stranger26]

Postal Code validation for Malaysia & Singapore

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)

[codecov]

Codecov Report

Merging #1502 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1502   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files          96       96           
  Lines        1277     1277           
=======================================
  Hits         1276     1276           
  Misses          1        1           

Impacted Files	Coverage Δ
src/lib/isPostalCode.js	100.00% <ø> (ø)

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[profnandaa]

LGTM, thanks for your contrib! 🎉