Changed download version back to 3.12 until the latest version is available on cdnjs

index.html

@@ -188,7 +188,7 @@
                     </p>
                     <h3>download</h3>
                     <p>
-                        <a href="download/vis.zip">vis.zip (version <span class="version">4.0.0</span>)</a>
+                        <a href="download/vis.zip">vis.zip (version <span class="version">3.12.0</span>)</a>
                     </p>
                 </div>
             </div>