Bust sponsors image cache

sponsors.md

@@ -7,7 +7,7 @@ title: Sponsors
   {% assign company = site.data.companies[sponsor] %}
   <li class="sponsors-listitem">
     <a href="{{ company.url }}" class="sponsors-link" target="_blank">
-      <img src="{{ company.image }}" alt="{{ company.name  }}"/>
+      <img src="{{ company.image | image_asset | buster }}" alt="{{ company.name }}"/>
     </a>
   </li>
 {% endfor %}