Easing functions not having any effect in skitter

Question

I am using skitter to create a slideshow and it looks like the easing functions I provide with the easing_default key are not having any effect. Here is my code:

$('.skitter').skitter({
    auto_play: false,
    dots: false,
    velocity: 0.1,
    easing_default: 'linear'
});

I tried a lot of values for the easing property like 'easeInQuart' etc. and the animation always seemed to move forward in the same way. I even tried some invalid values like 'fdoijhrb' and it did not give any errors.

What am I doing wrong here?

The library adds easing effects like this in its source code:

var easing = (this.settings.easing_default == '') ? 'easeInQuad' : this.settings.easing_default;

Link to the API: https://skitter-slider.net/options.html

Link to fiddle: https://jsfiddle.net/85uqdxhr/

Thanks.