title: Best way to override the WooCommerce category list Walker
body: <p>What is the best way to override the <strong>woocomerce</strong> function that is in defined in the <strong>woocomerce</strong> plugins directory inside some class.
  For example I am wanted to change the function <code>start_el</code> declared in the class <code>WC_Product_Cat_List_Walker</code>. I can change the function code in the plugin directory by the changes remains until I upgrade the <strong>woocomerce</strong> plugin.
  How can I override it in my theme <code>functions.php</code> file?</p>