Reduce dependencies

Allow us to be a little more standalone so that we can run this as a CI task.
The location of the `jshint.yml` file is heavily geared toward working with Rails at present and this dependency should be loosened, as you've correctly pointed out in this PR. However I don't feel like this is best approach to achieving this.

How about something along the lines of:

```ruby
Jshint.configuration = '/path/to/jshint.yml'
```

Then from there I can go about loading them in from the custom path and falling back to the default?