share type definitions among libs

It seems type definitions cannot share among different lib file. Is this a bug or any other extra configurations are needed?

#### ./flow/dto/ProductDTO.js

```js
// @flow
export type ProductDTO = {
id: number,
name: string,
img: string,
}

export type TestState = {
products: Array,
}
```

#### ./flow/redux/ProductStates.js

```js
// @flow
// I even tried to import type { ProductDTO } from '../dto/ProductDTO';
export type ProductState = {
products: Array,
}
```

#### example.js

```js
// @flow
const Test1: TestState = {
products: ['xxx'], // flow error report here as expected
}

const Test2: ProductState = {
products: ['xxx'], // no error, it seems flow does not recognize ProductState
}
```

#### .flowconfig

...
[libs]
flow
...