Webpack resolver looks for custom webpack config in packages with jsnext:main

With a `.eslintrc` like

```
"settings": {
"import/resolver": {
"webpack": {
"config": "webpack.karma.config.js"
}
}
},
```

when I import

```
import {takeEvery} from 'redux-saga';
```

I get the error

```
Cannot find module '/path/to/project/node_modules/redux-saga/webpack.karma.config.js
```

When I remove the `jsnext:main` entry from the `package.json` inside `node_modules/redux-saga`, the error goes away. So I guess the plugin is somehow trying to find a Webpack config inside `redux-saga` to load `resolve` configuration for ES6 files? This might be fine, looking for my custom Webpack config does not make sense, though.

Start with the reported .eslintrc resolver configuration and the package.json containing jsnext:main, then reproduce the import of redux-saga. Trace how the webpack resolver chooses and loads webpack.karma.config.js; done means the resolver no longer searches for that config inside the dependency and the import succeeds.

Written by the indexing model from the issue text.