fix(Toolbar): fix formatting of stacked example

Author: mfrances17

packages/react-core/src/components/Toolbar/examples/Toolbar.md

@@ -113,7 +113,7 @@ When all of a toolbar's required elements cannot fit in a single line, you can s
 
 ```
 
-## Background color variants
+### Background color variants
 
 To change the background color of a toolbar, use the `colorVariant` property on the `<Toolbar>`.