[v6] Minor request

[cristianocca]

@tannerlinsley I know you are no longer supporting v6, but it's still a wonderful library and migration to v7 is still unlikely for us.

I wonder if you could spare some time to fix some lifecycle methods, such as componentWillMount has been renamed... and release a minor update for react-table-v6. I understand we could fork it and fix it ourselves, but since hooks are still not "dead" and won't for the foreseeable future, it would be great to have v6 still support the right lifecycle methods.

Thanks.