Use h5 for callouts so that they are not included in ToC.

Callouts are already excluded from ToC, but due to a limitation in jekyll-toc they are still being included.

We should revisit this if the bug is fixed later.

site/docs/4.1/utilities/colors.md

@@ -49,7 +49,7 @@ When `$enable-gradients` is set to `true` (default is `false`), you can use `.bg
 - `.bg-gradient-{{ color.name }}`{% endfor %}
 
 {% capture callout %}
-#### Dealing with specificity
+##### Dealing with specificity
 
 Sometimes contextual classes cannot be applied due to the specificity of another selector. In some cases, a sufficient workaround is to wrap your element's content in a `<div>` with the class.
 {% endcapture %}