useFieldArray isn't exported

### Are you submitting a **bug report** or a **feature request**?

bug report

### What is the current behavior?

Hook useFieldArray isn't exported from index

### What is the expected behavior?

It should be exported

### What's your environment?

    "final-form": "4.13.1",
    "final-form-arrays": "1.1.2",
    "react-final-form": "6.0.1",
    "react-final-form-arrays": "3.0.0",
