feat(isPostalCode): add support for DO and HT

[yomed]

Added support to isPostalCode for The Dominican Republic and Haiti.

Checklist

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

[codecov]

Codecov Report

Merging #1456 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1456   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files          96       96           
  Lines        1275     1275           
=======================================
  Hits         1274     1274           
  Misses          1        1           

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

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7916dfd...8904d5d. Read the comment docs.

[profnandaa]

LGTM, thanks for your contribution! 🎉