Renamed skeleton/.gitignore to gitignore

> Did you know? The `.gitignore` inside `skeleton/` was actually affecting
> `twitter_ebooks`'s repo. This fixes that by moving it for `twitter_ebooks`,
> and moving it back when people make their repositories!

I have to admit that I didn't test this because I'm not even sure how to test it. So hopefully @mispy can double check this super important line and make sure it actually does what I think it does! ^^

```ruby
FileUtils.mv(File.join(path, 'gitignore'), File.join(path, '.gitignore'))
```