Update option-passing for creating child views.

IPython/html/static/notebook/js/widgets/widget.js

@@ -192,11 +192,11 @@ function(widget_manager, underscore, backbone){
             // triggered on model change
         },
 
-        child_view: function(model_id, view_name, options) {
+        child_view: function(model_id, options) {
             // create and return a child view, given a model id for a model and (optionally) a view name
             // if the view name is not given, it defaults to the model's default view attribute
             var child_model = this.widget_manager.get_model(model_id);
-            var child_view = this.widget_manager.create_view(child_model, view_name, options);
+            var child_view = this.widget_manager.create_view(child_model, options);
             this.child_views[model_id] = child_view;
             return child_view;
         },