mapbox.js terrain-rgb hillshade

Hillshading with mapbox.terrain-rgb
I used the example from https://www.mapbox.com/blog/terrain-rgb/ and just changed the conditionals in js/imagedata.js

<html>
  <head>
    <meta charset='UTF-8'>
    <title>Hillshade from terrain-rgb: mapbox.js</title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no,minimal-ui' />
    <link rel='stylesheet' href='//www.mapbox.com/base/latest/base.css'>
    <style>
      body {
        margin:0;
        padding:0;
      }
      #map {
        margin: 0;
        padding: 0;
        width:100%;
        height:100%;
      }
      .maphold {
        width: 100%;
      }
      .overlay {
        fill: none;
        pointer-events: all;
      }
    </style>
    </head>
  <body>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.mapbox.com/mapbox.js/v2.4.0/mapbox.js'></script>
    <link href='https://api.mapbox.com/mapbox.js/v2.4.0/mapbox.css' rel='stylesheet' />

https://api.mapbox.com/mapbox.js/v2.4.0/mapbox.js