query string?

Can this be solved? When testing with http://gtmetrix.com I get this:

Resources with a “?” in the URL are not cached by some proxy caching servers. Remove the query string and encode the parameters into the URL for the following resources:

http://piani.se/wp-content/plugins/woocommerce/assets/css/woocommerce-layout.css?ver=2.1.5
http://piani.se/wp-content/plugins/woocommerce/assets/css/woocommerce-smallscreen.css?ver=2.1.5
http://piani.se/wp-content/plugins/woocommerce/assets/css/woocommerce.css?ver=2.1.5
http://piani.se/wp-content/plugins/woocommerce/assets/js/frontend/cart-fragments.min.js?ver=2.1.5
http://piani.se/wp-content/plugins/woocommerce/assets/js/frontend/woocommerce.min.js?ver=2.1.5
http://piani.se/wp-content/plugins/woocommerce/assets/js/jquery-blockui/jquery.blockUI.min.js?ver=2.60
http://piani.se/wp-content/plugins/woocommerce/assets/js/jquery-cookie/jquery.cookie.min.js?ver=1.3.1

https://wordpress.org/plugins/woocommerce/