8 – Additional attribute for menu link

How I can add iteprop="url" for each link () in main menu?

So, I need to get from

<a href="http://drupal.stackexchange.com/node/114" data-drupal-link-system-path="node/114">Test</a>

to

<a href="http://drupal.stackexchange.com/node/114" data-drupal-link-system-path="node/114" itemprop="url">Test</a>

Is it possible to do it in preprocess? I would like not to use any module for this.