fix reverse of previous issue where stuck element would unstick too early if it has a top offset
Calculate yAxis for footer comparison off cssPosition.top + scrollTop rather than elements offset().top

fixes a flickering issue when scrolling upwards since the offset().top
may not have yet been properly calculated and creates a false positive
for sticking the element.
Merge pull request #2 from theshortcut/master

Scrolling upwards when past footer flicker and element with topOffset unsticking too early.