Upgrade to eslint 4

[benmccann]

I had to add one extra set of parentheses. I filed as an eslint bug for that one: eslint/eslint#9285

Otherwise I fixed all the issues in past PRs

[simonbrunel]

Do we really want to upgrade to ESLint 4 if it's bugged and forces us a syntax we don't want? what are the benefits?

[benmccann]

ESLint 4 found a good number of real issues as well. I fixed all those in a separate commit earlier: f6b6956

It's only this one place in the code base that there was a regression in behavior. I think all the real issues it found may outweigh having to add parens in one spot

[benmccann]

I've updated this to use the newest eslint with a fix for the bug I reported. It now passes locally without needing the extra set of parens

It's still failing on codeclimate. It must not be using the latest version of eslint. I've sent a PR to upgrade codeclimate: qltysh-archive/codeclimate-eslint#326

[benmccann]

@simonbrunel I now have eslint 4 working both locally and on codeclimate without any code formatting changes. You should be able to merge this PR now. Thanks for the review and feedback

[benmccann]

@etimberg @simonbrunel would we be able to merge this now? Even if we want to have a 2.7.2 I think this PR should still be okay

[etimberg]

I am ok with this