Use callout without custom Jekyll plugin.

docs/4.0/getting-started/webpack.md

@@ -30,9 +30,10 @@ Bootstrap is dependent on [jQuery](https://jquery.com/) and [Popper](https://pop
 these are defined as `peerDependencies`, this means that you will have to make sure to add both of them
 to your `package.json` using `npm install --save jquery popper.js`.
 
-{% callout warning %}
+{% capture callout %}
 Notice that if you chose to **import plugins individually**, you must also install [exports-loader](https://github.com/webpack-contrib/exports-loader)
-{% endcallout %}
+{% endcapture %}
+{% include callout.html content=callout type="warning" %}
 
 ## Importing Styles