Fixed Timeline.setGroups for Array (#2529)

lib/timeline/Timeline.js

@@ -271,13 +271,11 @@ Timeline.prototype.setGroups = function(groups) {
     newDataSet = null;
   }
   else {
-    var filter = {
-      filter : function(group){
-        return group.visible !== false;
-      }
+    var filter = function(group) {
+      return group.visible !== false;
     }
     if (groups instanceof DataSet || groups instanceof DataView) {
-      newDataSet = new DataView(groups,filter);
+      newDataSet = new DataView(groups,{filter: filter});
     }
     else {
       // turn an array into a dataset