Changing name prop doesn't change mutator functions

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

Bug Report

### What is the current behavior?

Changing the `name` prop does not update the field with the new name's value. All mutators are called on the original data set.

### What is the expected behavior?

Changing the name should change the fields modified by the mutator.

### Sandbox Link

https://codesandbox.io/s/react-final-form-field-arrays-h3kdl

To reproduce:

1. Add two customers (`customers[x]`)
2. Click "Toggle Field Name"
3. Add two more customers (`customers2[x]`)
4. Click their delete buttons. They delete `customers[x]` instead of `customers2[x]`.

This example is contrived, but my use case is not: I have tabs which change the `name` value passed into the FieldArray prop's render component to allow for localization of similar values. This behavior, for whatever it's worth, diverges from `redux-form` where similar code worked fine.

### What's your environment?

```
"final-form": "^4.18.7",
"final-form-arrays": "^3.0.2",
"react-final-form": "^6.3.3",
"react-final-form-arrays": "^3.1.1",
```

Chrome 80, macOS Mojave 10.14.6

### Other information

When `useFieldArray` is first called, `useConstant` is called and ensures this code really, really never runs again...

https://github.com/final-form/react-final-form-arrays/blob/master/src/useFieldArray.js#L34

It curries the `name` prop in to all mutators. This means that even if `name` changes over time, it will still mutate the original set. This seems to be the source of the issue, but I could not begin to know how to resolve without truly changing the way the plugin works and likely breaking something.