Update code-splitting.md (#546)

content/docs/code-splitting.md

@@ -100,7 +100,7 @@ import("./math").then(math => {
 > part of the language standard. It is expected to be accepted within the
 > near future.
 
-When Webpack comes across this syntax, it automatically start code-splitting
+When Webpack comes across this syntax, it automatically starts code-splitting
 your app. If you're using Create React App, this is already configured for you
 and you can [start using it](https://github.com/facebookincubator/create-react-app/blob/master/packages/react-scripts/template/README.md#code-splitting) immediately. It's also supported
 out of the box in [Next.js](https://github.com/zeit/next.js/#dynamic-import).