Inferred Import Fails But Explicit Import Succeeds

Explicity passing my webpack resolve object means ESLint can correctly resolve aliased paths:

.eslint.js
```
"settings": {
"import/resolver": {
"webpack": {
"config": {
"resolve": {
"modules": ["app", "node_modules"],
"extensions": [".js", ".jsx", ".css"],
"alias": {
"component-styles": "css/components",
},
}
}
}
}
}
```

However using configuration that infers paths fails:

.eslint.js
```
"settings": {
"import/resolver": "webpack"
}
```

or:

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

In both cases, paths aren't discovered

Webpack 2.2.0
eslint-plugin-import 2.2.0

Start by reproducing the two inferred configurations in .eslint.js, comparing them with the explicit webpack resolve object shown in the issue. Trace how the webpack resolver discovers configuration and aliases; done means both inferred forms resolve the same aliased paths successfully.

Written by the indexing model from the issue text.