slick-active not correctly set for uneven sets if slidesToScroll=slidesToShow

If you have an uneven set and slidesToScroll=slidesToShow the slick-active class is not correctly set for the set of slides where the last slides are shown, e.g. on http://kenwheeler.github.io/slick/ you have this problem in the uneven demo when slides 3, 4, 5, 6 are being shown. 

Hope this is the right place to fix it, but maybe it might be related to the index.