Omit ESLint warnings when there are ESLint errors

Created by: gaearon

This fixes https://github.com/facebookincubator/create-react-app/issues/2056. It's not really maintainable—I'll file another issue to rewrite this to a custom ESLint formatter.

Just warnings:

Now I make an error:

(Before, they would all be displayed together.)

After fixing the error:

Merged by: gaearon at 2017-05-11 12:58:07 UTC

Created by: midudev

Maybe would be better to first show errors and then show any the warnings, instead remove completely them. What do you think?

Created by: gaearon

Maybe, but it's kinda hard to do with current implementation. Maybe we can do it after https://github.com/facebookincubator/create-react-app/issues/2121.

Regardless, we only use errors for things that are guaranteed to break your code, and that you must fix straight away. I've seen beginners get overwhelmed by warning screen, and I want to avoid the mental overhead when you need to focus on getting your code to work again.