title: Gmaps4Rails - custom infowindow not working
body: <p>I'm having trouble implementing a custom infobox on rails using the Google Maps 4 Rails gem.
  I've added the infobox plugin to the top of the page and tried the code snippet in the docs, but still no custom infobox or a class of "yellow" on the infobox window.</p>
  
  <p>How do I pass options for the custom infobox to the markers being generated by the following?</p>
  
  <pre><code>:javascript
   handler = Gmaps.build('Google');
   handler.buildMap({ provider: {
     }, internal: {id: 'map'}}, function(){
     markers = handler.addMarkers(#{raw @hash.to_json},{builders: {Marker: InfoBoxBuilder}});
     handler.bounds.extendWith(markers);
     handler.fitMapToBounds();
     handler.getMap().setZoom(9);
    });    
  </code></pre>
  
  <p>I also added the following code to infowindow.js.coffee</p>
  
  <pre><code>class InfoBoxBuilder extends Gmaps.Google.Builders.Marker # inherit from base builder
  
  # override method
  create_infowindow: -&gt;
    return null unless _.isString @args.infowindow
    boxText = document.createElement("div")
    boxText.setAttribute("class", 'yellow') #to customize
    boxText.innerHTML = @args.infowindow
    @infowindow = new InfoBox(@infobox(boxText))
  
  infobox: (boxText)-&gt;
    content: boxText
    pixelOffset: new google.maps.Size(-140, 0)
    boxStyle:
    width: "280px"
  
  handler = Gmaps.build 'Google', { builders: { Marker: InfoBoxBuilder} }
  </code></pre>
  
  <p>Any help would be much appreciated. Thank you.</p>