Explicitly specify ESLint config path for editor plugins in package.json

Created by: keyz

Fixes #124 (closed). Notice that we need to change the path in package.json while ejecting since the config folder gets moved.

Tested with Atom (Nuclide) and Visual Studio Code and it works both before and after ejection. I'm not sure about Sublime Text -- seems like SublimeLinter-eslint only recognizes .eslintrc config. However, it could be fixed by configuring the linter plugin itself. Or even better, could someone who uses Sublime Text send a PR to let it recognize the eslintConfig field in package.json? :)

Edit: @kevinastone confirmed that Sublime Text works fine too.