Field Arrays example not works with latest versions of packages

Field Arrays example not works with latest versions of packages

```
{
"name": "react-final-form-field-arrays",
"version": "1.0.0",
"description": "This example demonstrates how to use helper packages final-form-arrays and react-final-form-arrays to manage array fields.",
"keywords": [],
"main": "index.js",
"dependencies": {
"styled-components": "2.2.4",
"react-final-form-arrays": "^2.0.1",
"react-final-form": "^3.6.7",
"react-dom": "16.2.0",
"react": "16.2.0",
"final-form-arrays": "^1.1.0",
"final-form": "^4.10.0"
}
}
```

But it works good with `"react-final-form-arrays": "1.0.0"`

### Sandbox Link
https://codesandbox.io/s/vn1y5nrpv5