title: How to fix 'stop.at is not a function' error?
body: <p>With v2.5 it's ok, but v3 say "stop.at is not a function" when I try define the gradient.</p>
  
  <pre><code>&lt;svg id="svg1"&gt; &lt;/svg&gt;
  
  var draw = SVG('#svg1').size(100,100);
  var linear = draw.gradient('linear', function(stop) {
    stop.at(0, '#f06', 1);
    stop.at(1, '#0f9', 1);
  });
  
  draw.rect(100, 100).fill( linear );
  </code></pre>