fixing issue with fonts that doesn't download

Basically, I revert the commit e8b3376456aabb33a1fa6cfecdff014a17c89984 .

I get the @Fort-Awesome/Font-Awesome repo in my machine, and start looking at the files. In the fontawesome repo the fonts are with +x permission. I do the same here, test across my applications, and it's working like a charm.

If someone else want to try it, change your Gemfile to:

```
gem 'font-awesome-sass-rails', github: 'caarlos0/font-awesome-sass-rails'
```

This fixes issue #22.

Hope it helps.