Changing infowindow offset with CartoDB.js

<!DOCTYPE html>
<html>
  <head>
    <title>Custom infowindow example | CartoDB.js</title>
    <meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
    <meta http-equiv="content-type" content="text/html; charset=UTF-8"/>
    <link rel="shortcut icon" href="https://cartodb.com/assets/favicon.ico" />
    
    <style>html, body, #map { height: 100%; padding: 0; margin: 0 }</style>
    <link rel="stylesheet" href="https://libs.cartocdn.com/cartodb.js/v3/themes/css/cartodb.css" />
  </head>
  <body>
    <div id="map"></div>

<script src="https://libs.cartocdn.com/cartodb.js/v3/cartodb.js"></script>
    
    <script type="text/javascript">
      var layer;

function main() {

var map = L.map('map', { 
          zoomControl: false,
          center: [43, -3],
          zoom: 3
        });

// add a nice baselayer from Stamen 
        L.tileLayer('https://a.tiles.mapbox.com/v3/examples.map-20v6611k/{z}/{x}/{y}.png', {
          attribution: 'MapBox'
        }).addTo(map);

cartodb.createLayer(map, 'https://documentation.cartodb.com/api/v2/viz/2b13c956-e7c1-11e2-806b-5404a6a683d5/viz.json')
          .addTo(map)
          .on('done', function(lyr) {
            lyr.getSubLayer(0).infowindow.set({
              offset: [28,20],
              template: $('#infowindow_template').html(),
              width: 350,
              maxHeight: 400
            });
          }).on('error', function() {
            console.log("some error occurred");
          });
      }

window.onload = main;
      
    </script>
  </body>
</html>

Modified http://libs.cartocdn.com/cartodb.js/v3/cartodb.js to a secure url

https://libs.cartocdn.com/cartodb.js/v3/cartodb.js