[uk] Updated and renamed locale

Rename to ```uk```, because it's commonly used to denote Ukrainian language. For example it's used by such projects as:
- original [select2](https://github.com/ivaynberg/select2/blob/master/select2_locale_uk.js);
- [rails-i18n](https://github.com/svenfuchs/rails-i18n/blob/master/rails/locale/uk.yml) and this causes an error if we try to use ```ua``` instead;
- [Google Translate](http://translate.google.com.ua/#en/uk/Hi);
- [Wikipedia](http://uk.wikipedia.org/);