Fixed radio button selector for new radio button class

IPython/html/tests/widgets/widget_selection.js

@@ -8,7 +8,7 b' casper.notebook_test(function () {'
 
     var combo_selector = '.widget-area .widget-subarea .widget-hbox-single .btn-group .widget-combo-btn';
     var multibtn_selector = '.widget-area .widget-subarea .widget-hbox-single .btn-group[data-toggle="buttons-radio"]';
-    var radio_selector = '.widget-area .widget-subarea .widget-hbox .vbox';
+    var radio_selector = '.widget-area .widget-subarea .widget-hbox ..widget-radio-box';
     var list_selector = '.widget-area .widget-subarea .widget-hbox .widget-listbox';
 
     var selection_index;