Move Jquery.js to Footer

When you deregister jQuery, you have to register it again. Try this code

UPDATE: You have to deregister jQuery first (first part of your code), so the final code should be:

//Load on Footer
add_action('wp_enqueue_scripts', 'register_jquery');
function register_jquery() {
    wp_deregister_script('jquery'); // remove original jQuery
    wp_register_script( // add custom jQuery in footer
       'jquery', 
       'https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js',
       array(), // dependencies
       null, // version
       true); // load in footer?
    wp_enqueue_script('jquery');
}

But it’s NOT RECOMMENDED to load custom jquery in wordpress.