Fix link to "Output widget examples"

The space in the URL disrupts the Markdown syntax so that the hyperlink isn't rendered properly. This replaces the space with `%20` to fix the link.

docs/source/examples/Widget List.ipynb

@@ -956,7 +956,7 @@
    "source": [
     "## Output\n",
     "\n",
-    "The `Output` widget can capture and display stdout, stderr and [rich output generated by IPython](http://ipython.readthedocs.io/en/stable/api/generated/IPython.display.html#module-IPython.display). For detailed documentation, see the [output widget examples](https://ipywidgets.readthedocs.io/en/latest/examples/Output Widget.html)."
+    "The `Output` widget can capture and display stdout, stderr and [rich output generated by IPython](http://ipython.readthedocs.io/en/stable/api/generated/IPython.display.html#module-IPython.display). For detailed documentation, see the [output widget examples](https://ipywidgets.readthedocs.io/en/latest/examples/Output%20Widget.html)."
    ]
   },
   {