Update code to work with newer Jupyter versions

Author: guoci

chapter03_notebook/03_widgets.ipynb

@@ -345,7 +345,10 @@
    "source": [
     "@button.on_click\n",
     "def plot_on_click(b):\n",
-    "    plot2()"
+    "    out.clear_output(wait=True)\n",
+    "    with out:\n",
+    "        plot2()\n",
+    "        plt.show()"
    ]
   },
   {
@@ -385,10 +388,11 @@
     }
    ],
    "source": [
+    "out = widgets.Output()\n",
     "tab = widgets.Tab(children=[tab1, tab2])\n",
     "tab.set_title(0, 'plot')\n",
     "tab.set_title(1, 'styling')\n",
-    "VBox(children=[tab, button])"
+    "VBox(children=[tab, button, out])"
    ]
   }
  ],