Properly load jQuery from Google CDN - change version accordingly

wordpress-enqueue-jquery.php

function jquery_cdn() {
   if (!is_admin()) {
      wp_deregister_script('jquery');
      wp_register_script('jquery', 'http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js', false, '1.8.3');
      wp_enqueue_script('jquery');
   }
}
add_action('init', 'jquery_cdn');