Contribute back our version of the flag of Serbia

[Wyatt OʼDay]

See commit 825b965

Update Flag of Serbia (use Pantone colors from "На основу члана 9. став 1. Закона о изгледу и употреби грба, заставе и химне Републике Србије / Pursuant to Article 9, paragraph 1 of the Law on the Appearance and Use of the Coat of Arms, Flag and Anthem of the Republic of Serbia").

https://www.srbija.gov.rs/extfile/sr/142564/uredba_izvornik_grba_zastave_himne0355_cyr.zip

Backup of "uredba_izvornik_grba_zastave_himne0355_cyr.zip" in case original link dies.

PANTONE 192 C, https://www.pantone.com/color-finder/192-C
Hex: #E40046

PANTONE 280 C, https://www.pantone.com/color-finder/280-C
Hex: #012169

PANTONE 123 C, https://www.pantone.com/color-finder/123-C
Hex: #FFC72C

Contribute back these changes here: https://commons.wikimedia.org/wiki/File:Flag_of_Serbia.svg