Problem with ajax-cart.js (Javascript and Jquery ...)

Hi !

I've just installed the newest upgrade of Marketpress and I have a big problem :

My javascript and my Jquery don't work since this upgrade. Firebug says :

"

TypeError: $(...).on is not a function

$(document).on('click', '#mp_product_nav a', function(){

"

on /wp-content/plugins/marketpress/marketpress-includes/js/ajax-cart.js?ver=2.8.1 (line 75)

What is this problem ?

I seen that these lines wasn't here in my previous marketpress version (2.6.4)...

Sincerly,