Vertical swipe sensitivity

[calebcng]

Hi, thanks for the great work on this package, it's been working great thus far! One issue I have noticed however is that often when swiping a card upwards following the natural arc'ed gesture of the thumb, swipes are incorrectly categorized as a Left or Right swipe rather than an upwards swipe.

Steps to reproduce:

1. Create a basic CardSwiper that allows both horizontal and vertical swipe directions
2. For the onSwipe parameter, add a simple print to display the swipe direction
   print('$previousIndex, $currentIndex, $direction');
3. Swipe card upwards, initially starting with a straight vertical motion, progressively increasing the angle of the swipe