default rule not being triggered with webpack resolver

When the `default` rule is applied, the resolved module with my current webpack setup is always evaluated as `null` [here](https://github.com/benmosher/eslint-plugin-import/blob/master/src/rules/default.js#L22)

```javascript
// src/rules/default.js
var imports = Exports.get(node.source.value, context)
if (imports == null) return
```

Since the imports variable is always `null`, the `default` rule never gets a chance to be evaluated.

For whatever reason, I can't figure out which combination of resolvers / webpack settings to use to get my modules to load correctly in the plugin... Any insight would be greatly appreciated!

Current eslintrc.yml
```yaml
parser: 'babel-eslint'
ecmaFeatures:
modules: true
jsx: true
parserOptions:
ecmaFeatures:
jsx: true
experimentalObjectRestSpread: true
sourceType: 'module'
ecmaVersion: 6
env:
browser: true
es6: true
jest: true
node: true
plugins: [ 'react', 'import' ]

settings:
import/resolver:
webpack:
config: './webpack.dev.js'
...
```

Start with src/rules/default.js at line 22 and inspect how the webpack resolver is configured through the shown eslintrc.yml settings and webpack.dev.js. Reproduce the null result with the documented resolver setup, then verify that the default rule is evaluated with the resolved module instead of being skipped.

Written by the indexing model from the issue text.