Fix mixed content warning

Author: theel0ja

index.html

@@ -3395,7 +3395,7 @@ <h2 id="changelog">Change Log</h2>
 
       <p>
         <a href="http://documentcloud.org/" title="A DocumentCloud Project" style="background:none;">
-          <img src="http://jashkenas.s3.amazonaws.com/images/a_documentcloud_project.png" alt="A DocumentCloud Project" />
+          <img src="https://jashkenas.s3.amazonaws.com/images/a_documentcloud_project.png" alt="A DocumentCloud Project" />
         </a>
       </p>