feat((isPostalCode): Added postal code for Turkey

[Joereaver]

Added the postal code for Turkey in isPostalCode.js. Also added TR: to the test to include valid and invalid examples.

(https://en.wikipedia.org/wiki/Postal_codes_in_Turkey)

Checklist

• [x ] PR contains only changes related; no stray files, etc.
• [x ] README updated (where applicable)
• [x ] Tests written (where applicable)
• [x ] References provided in PR (where applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9ff3424) to head (1bc036b).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2894   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2599      2599           
  Branches       658       658           
=========================================
  Hits          2599      2599           

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