Expo + react-native-fs

## Description
In my application I am not able to run it with linked modules.

## Expected Behavior

React native should link module.

## Observed Behavior

I need to open files from local system. In npm, there is library like `react-native-fs` but still receive error.

```
undefined is not an object (evaluating 'RNFSManager.RNFSFileTypeRegular')
```

How to add module?
1. `npm install react-native-fs`
2. `react-native link react-native-fs`

It seems that expo ignores "linked" modules to react-native.