Fix for infinitely large carousels in Chrome.

In Chrome in certain circumstances, the slick-list div does not provide the expected overflow:hidden behaviour. Has been seen on both desktop and Android versions of chrome.

Instead, it grows as wide as slick-track does. Due to this, every time the widths are recalculated the list is wider, and the widths get even greater as they're taken as a fraction of the list width (we've seen millions of px).

This pull request sets the max-width on the list to the width needed, stopping this issue from happening, but not breaking any existing behaviour.