fix: update bosnian, BA postal code

[zlayabekrija]

Adding Bosnian (BA) zip/postal code validator.

• Updated isPostalCode method with 'BA' key and appropriate regex validator
• Updated tests to verify solution
• Updated ReadMe with given key

Checklist

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

[codecov]

Codecov Report

Merging #1956 (bd1f22c) into master (c1b21a9) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #1956   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          102       102           
  Lines         2085      2085           
  Branches       472       472           
=========================================
  Hits          2085      2085           

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

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[tux-tn]

Thank you for your PR @zlayabekrija !
LGTM 🎉

[zlayabekrija]

Thanks a lot <3

[profnandaa]

LGTM. Thanks for your contrib! 🎉