Don't modify available locales app

If you use information of ``` I18n.available_locales ``` in your app you probably wouldn't modify this information for keep original behaviors of your features, but in loading ``` devise-i18-n ``` gems your ``` I18n.available_locales ``` became :

```
=> [:en, :ar, :az, :bg, :ca, :cs, :da, :de, :el, :"en-GB", :es, :et, :fa, :fi, :fr, :he, :hr, :hu, :id, :is, :it, :ja, :ko, :lt, :lv, :my, :nb, :nl, :no, :pl, :"pt-BR", :pt, :ro, :ru, :sk, :sl, :sv, :th, :tr, :uk, :vi, :"zh-CN", :"zh-HK", :"zh-TW"]
```

it's little much more for my little application ;-)