Subscriptions in FieldArray aren't work correctly

### Are you submitting a **bug report** or a **feature request**?
Yes

### What is the current behavior?
Subscriptions in FieldArray aren't work correctly.

### What is the expected behavior?
In none FieldArray components the subscriptions are working very nice, but in field array like
```
{
"active": false,
"dirty": false,
"dirtySinceLastSubmit": false,
"invalid": true,
"name": "customers",
"pristine": true,
"touched": false,
"visited": false
}
```
are not working correctly.

### Sandbox Link
[](https://codesandbox.io/s/pyxloppr70?fontsize=14)

### What's your environment?

```
{
"final-form": "4.11.1",
"final-form-arrays": "latest",
"react": "16.8.3",
"react-dom": "16.8.3",
"react-final-form": "4.0.2",
"react-final-form-arrays": "2.0.1",
"styled-components": "4.1.3"
}
```

Start with the linked CodeSandbox reproduction and compare subscription behavior in ordinary fields with the FieldArray example. Review the listed final-form, final-form-arrays, react-final-form, and react-final-form-arrays versions while isolating the differing state updates. Done means the FieldArray subscription reports the expected state consistently, with a regression test added if the project’s test entry point is identified.

Written by the indexing model from the issue text.