Update glob to include locales again

On current master the files in `rails/locale/`are not added to the gem. As result no translations are available.

```
$ gem build i18n-country-translations.gemspec
$ gem spec i18n-country-translations-1.1.1.gem
...
files:
- MIT-LICENSE
- README.rdoc
- lib/i18n-country-translations.rb
- lib/i18n_country_translations.rb
- lib/i18n_country_translations/railtie.rb
- lib/i18n_country_translations/version.rb
- lib/tasks/i18n-country-translations_tasks.rake
homepage: https://github.com/onomojo/i18n-country-translations
...
```

With the change:

```
$ gem build i18n-country-translations.gemspec
$ gem spec i18n-country-translations-1.1.1.gem
...
files:
- MIT-LICENSE
- README.rdoc
- lib/i18n-country-translations.rb
- lib/i18n_country_translations.rb
- lib/i18n_country_translations/railtie.rb
- lib/i18n_country_translations/version.rb
- lib/tasks/i18n-country-translations_tasks.rake
- rails/locale/iso_639-1/af.yml
- rails/locale/iso_639-1/ak.yml
- rails/locale/iso_639-1/am.yml
- rails/locale/iso_639-1/ar.yml
- rails/locale/iso_639-1/as.yml
- rails/locale/iso_639-1/az.yml
...
```