sorting is not toggled properly when used with custom 'sortType' callback function

Using v7

Hi there! First of all thanks for all your efforts in creating such a great library.

Bug Description I did encounter a rather strange problem with the latest version (v7.0.0-rc.16): when I use a custom function for sorting, the results are sorted for one direction only. P.S: same code works fine with v7.0.0-rc.15

Additional context here is the code for the custom sorting function

const sortHelper = ({
	isAfter,
	isBefore,
	desc
}) => {
	let order

	if (isAfter) {
		order = 1
	} else if (isBefore) {
		order = -1
	} else {
		order = 0
	}

	if (desc) {
		return -order
	} else {
		return order
	}
}

const sortString = (rowA, rowB, columnId, desc) => {
	const stringA = rowA.values[columnId].trim().toLowerCase()
	const stringB = rowB.values[columnId].trim().toLowerCase()

	const isAfter = stringA > stringB
	const isBefore = stringA < stringB

	return sortHelper({
		isAfter,
		isBefore,
		desc
	})
}

here the code for the table component

const OverviewTable = (props) => {
	const columns = [
		{
			Header: <span>{translate({ text: 'FIRSTNAME' }).text}</span>,
			accessor: 'firstname',
			sortType: sortString
		},
		{
			Header: <span>{translate({ text: 'LASTNAME' }).text}</span>,
			accessor: 'lastname',
			sortType: sortString
		}
	]

	const data = props.data

	return (
		<Table columns={columns} data={data} />
	)
}

[gargroh]

Sort Comparator function should return -1 || 0 || 1.

Boolean will not work.

[tannerlinsley]

@mattstates, please ask your question in https://spectrum.chat/react-table 😃 Thanks!