Corrected Ukrainian locale.

`uk` is the correct [ISO 639-1 code](http://www.loc.gov/standards/iso639-2/php/English_list.php) for the Ukrainian language, while `ua` is the ccTLD for Ukraine.

![warning](https://f.cloud.github.com/assets/28428/2267582/165c4e60-9eba-11e3-87d1-bc7484722df0.png)

Ref: #164