/**
* Change jQuery version to older by wpdevkit.in
*/
function replace_core_jquery_version() {
    wp_deregister_script( 'jquery' );
    // Change the URL if you want to load a local copy of jQuery from your own server.
    wp_register_script( 'jquery', "https://code.jquery.com/jquery-3.0.0.min.js");
}
add_action( 'admin_enqueue_scripts', 'replace_core_jquery_version' );