Serbian's language flag is incorrect

Hello everyone!

I really love phalcon framework and I use it all the time.

I've noticed one small problem with Serbian's language flag and I hope you'll fix it.

This is the correct one:

https://static.phalconphp.com/images/flags/rs.gif

https://en.wikipedia.org/wiki/Serbia

not this one:

https://static.phalconphp.com/images/flags/sr.gif

Thanks!

Thanks, feel free to submit a PR to the website repo: https://github.com/phalcon/website