Update code-splitting.md (setup → set up) (reactjs#3643)

(`setup` is the noun form and `set up` is the verb form.)

content/docs/code-splitting.md

@@ -42,7 +42,7 @@ console.log(add(16, 26)); // 42
 
 If you're using [Create React App](https://create-react-app.dev/), [Next.js](https://nextjs.org/), [Gatsby](https://www.gatsbyjs.org/), or a similar tool, you will have a Webpack setup out of the box to bundle your app.
 
-If you aren't, you'll need to setup bundling yourself. For example, see the [Installation](https://webpack.js.org/guides/installation/) and [Getting Started](https://webpack.js.org/guides/getting-started/) guides on the Webpack docs.
+If you aren't, you'll need to set up bundling yourself. For example, see the [Installation](https://webpack.js.org/guides/installation/) and [Getting Started](https://webpack.js.org/guides/getting-started/) guides on the Webpack docs.
 
 ## Code Splitting {#code-splitting}