DOC: Avoid nested markup

nbsphinx doesn't support that yet, see
spatialaudio/nbsphinx#301

Author: mgeier

docs/source/examples/Widget Styling.ipynb

@@ -15,12 +15,12 @@
    "source": [
     "You can jump directly to these sections:\n",
     "\n",
-    "+ [The `layout` attribute](#The-layout-attribute)\n",
+    "+ [The layout attribute](#The-layout-attribute)\n",
     "+ [The Flexbox layout](#The-Flexbox-layout)\n",
     "+ [Predefined styles](#Predefined-styles)\n",
-    "+ [The `style` attribute](#The-style-attribute)\n",
+    "+ [The style attribute](#The-style-attribute)\n",
     "+ [The Grid layout](#The-Grid-layout)\n",
-    "+ [`Image` layout and sizing](#Image-layout-and-sizing)"
+    "+ [Image layout and sizing](#Image-layout-and-sizing)"
    ]
   },
   {