no-duplicates should ignore flow type imports

I'm using [flow](http://flowtype.org/) and `no-duplicates` triggers on:

``` js
import {someFunction} from '../src/foo';
import type {someType} from '../src/foo';
```

But as far as I know there's no way to import both types and other exports with the same line. `no-duplicates` should consider a flow type import as separate from a module export.
