webpack.md: Replace "both of them" with "it" (#31794)

 Yay! I helped!

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

site/content/docs/5.0/getting-started/webpack.md

@@ -27,7 +27,7 @@ import Alert from 'bootstrap/js/dist/alert';
 {{< /highlight >}}
 
 Bootstrap depends on [Popper](https://popper.js.org/), which is specified in the `peerDependencies` property.
-This means that you will have to make sure to add both of them to your `package.json` using `npm install popper.js`.
+This means that you will have to make sure to add it to your `package.json` using `npm install popper.js`.
 
 ## Importing Styles