One Page WordPress Site scrollTo problem.. Help!

I've managed to follow along on Zac's video for the one page wordpress site on a different theme called (stork) which i've started to customise via a child theme, but i just cannot get the 'scroll to' jquery feature to work with the links.

Please take a look at my site to see if you can work it out.. i'm slowly trying to create a portfolio for myself and currently on the web design track, but have not yet reached JS.

garryc.me

i've added theme.js to the js directory and here is the code -

/**
* Custom Theme Styles
*/

( function( $ ) {

    $("nav a").click(function() {
        var link = $(this).attr('href');
    $('html, body').animate({
        scrollTop: $(link).offset().top
    }, 2000);
});

} )( jQuery );

i've added the link to this js file through WP_enqueue in functions.php

wp_enqueue_script( 'jgtstork-script-custom', get_template_directory_uri() . '/js/theme.js', array( 'jquery' ), '', true );

This can be seen on my site when clicking inspect element like Zac does in the video.. but i just cannot seem to figure it out its not scrolling slow to each link.

Where have I gone wrong?!