Support for .eslintignore

[doits]

It would be nice if the .eslintignore was respected.

[mmozuras]

@doits it seems a better fit to handle it on eslintrb instead of Pronto? Have you considered it?

[doits]

Yeah, maybe that's a better place. But since I am now using my own runner https://github.com/doits/pronto-eslint_npm, where it works out of the box, I do not need this any more in here or in eslintrb.