Fixed missing SK locale for isPostalCode

[tfilo]

In source code you already support SK locale for few years, but it was missing in documentation.
validator.js/src/lib/isPostalCode.js

Fixed missing SK locale for isPostalCode in readme file.

Fixed missing SK locale for isPostalCode in readme file.

Checklist

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

[codecov]

Codecov Report

Merging #1957 (9e04886) into master (0175670) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #1957   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          103       103           
  Lines         2099      2099           
  Branches       474       474           
=========================================
  Hits          2099      2099           

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[tux-tn]

Nice catch! Thank you for your PR @tfilo
LGTM 🎉

[profnandaa]

Thanks for the catch, sorry we've a merge conflict coz of the other PR changes. Could you update?

[tfilo]

Thanks for the catch, sorry we've a merge conflict coz of the other PR changes. Could you update?

I did merge of master into my branch. Now it should have no conflict.