column option sortCompare is missing

## Expected Behavior

Providing a `sortCompare` callback to a column options (as described at the [documentation](https://github.com/gregnb/mui-datatables/blob/master/examples/column-sort/index.js)).

## Current Behavior

There's no actual sortCompare option: there is no reference at the declaration file and the callback is not called).

## Your Environment

| Tech | Version |
|--------------|---------|
| Material-UI | 4.9.9 |
| MUI-datatables | 3.2.0 |
| React | 4.0.5 |
| browser | Chrome 84 |