eslint: fix no-undef for static properties

[samouri]

@eliorivero today reported getting (false) no-undef warnings in eslint. It was caused by upgrading babel-eslint which has this bug in it. downgrading seems to fix it.

To Test

1. checkout this branch and do an npm install
2. run node_modules/.bin/eslint client/signup/step-wrapper/index.jsx. You shouldn't get any errors

[matticbot]

Test live: https://calypso.live/?branch=fix/babel-eslint-integration

[gwwar]

LGTM!

[gwwar]

Desktop breakage looks a little odd. Maybe we need to clear a cache?

Bundling app and server
fs.js:646
  return binding.open(pathModule._makeLong(path), stringToFlags(flags), mode);
                 ^

Error: ENOENT: no such file or directory, open '/Users/distiller/wp-desktop/calypso/.babelrc'
    at Object.fs.openSync (fs.js:646:18)
    at Object.fs.readFileSync (fs.js:551:33)
    at Object.<anonymous> (/Users/distiller/wp-desktop/webpack.shared.js:11:36)
    at Module._compile (module.js:643:30)

[eliorivero]

Works fine 🐑
Tested:

node_modules/.bin/eslint client/signup/step-wrapper/index.jsx                                                                                                                            

and got

The react/jsx-space-before-closing rule is deprecated. Please use the react/jsx-tag-spacing rule with the "beforeSelfClosing" option instead.

And also added a change like

static defaultProps = {
	foo: 'bar',
};

and committed, which is similar to the original case where I found this, and got no issues.

[jsnajdr]

@nosolosw tried to upgrade our eslint to 4.0 few months ago (around the GM) and had to revert it because of errors. And I'm pretty sure that it was something with class properties, too. Maybe exactly the same error.

If we resolve this, could we try the eslint 4.0 upgrade again soon?

[oandregal]

I'm at my support rotation this week, so I've got limited bandwith. FWIW, #18106 is the issue I ran into.

[oandregal]

Note that babel-eslint still reports that is not compatible with ESLint4, and the original issue is still open.