Add Serbian translations to countries.json (both common and official) (#534)

* Add Serbian translations for countries, common and official

Sources:
- [The Ministry of Foreign Affairs of the Republic of Serbia](https://www.mfa.gov.rs/spoljna-politika/bilateralna-saradnja);
- [Google Serbia](https://www.google.rs/);
- [Wikipedia Serbia](https://sr.wikipedia.org/wiki/%D0%93%D0%BB%D0%B0%D0%B2%D0%BD%D0%B0_%D1%81%D1%82%D1%80%D0%B0%D0%BD%D0%B0).

* Add cyrillic version for `altSpellings` of the country common name

Precisely: "Србија".

* Add the rebuild files to the dist folder using the `country.php` script

* Revert "Add the rebuild files to the dist folder using the `country.php` script"

This reverts commit 87f1d36.

* doc: add mention of Serbian translation to `CHANGELOG.md`

Author: zeravcic

CHANGELOG.md

@@ -6,6 +6,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- add Serbian translation (#534)
 ### Changed
 - add missing translations for Curaçao (Croatian) and Iran (Persian) (#496)
 - add missing Japanese translations for Curaçao and Kosovo (#498)