/**
 * Returns next indexed key based on passed index
 *
 * @access private
 *
 * @param {Number} $index - index of breakpoint
 *
 * @return {String}
 *
 * @group Internal Functions
 */
@function flint-next-index($index) {
	@return if(flint-is-number($index) and $index != 0, flint-steal-key($index + 1), false);
}