removed zip download and linked to github instead

index.html

@@ -223,7 +223,7 @@
                     </p>
                     <h3>download</h3>
                     <p>
-                        <a href="download/vis.zip">vis.zip (version <span class="version">4.17.0</span>)</a>
+                        <a href="https://github.com/almende/vis/archive/v4.17.0.zip">v4.17.0.zip</a>
                     </p>
                 </div>
             </div>