Update mini tutorial code to use api introduced in alpha3

tests/testbench/com/vaadin/tests/widgetset/client/minitutorials/v7a2/WidgetContainerConnector.java

@@ -16,7 +16,7 @@ public class WidgetContainerConnector extends
 
     @Override
     public void onConnectorHierarchyChange(ConnectorHierarchyChangeEvent event) {
-        List<ComponentConnector> children = getChildren();
+        List<ComponentConnector> children = getChildComponents();
         VWidgetContainer widget = (VWidgetContainer) getWidget();
         widget.clear();
         for (ComponentConnector connector : children) {