Now that you can choose to ignore them, fail lint if there are extra dependencies

@TabDigital/api 

If there's any dependencies in `package.json` that aren't actually used, it will print

```
[require-lint] Extraneous dependencies: coffee-script
```

This used to just be a warning, but now that you can choose to ignore them with `--ignore-extra coffee-script`, it's probably better to fail the build if there's any leftover ones.

*Note: breaking change, so we should bump up to 1.0.0*