Fix code highlight in tutorial (#3935)

docs/tutorial/part-four/index.md

@@ -1019,7 +1019,7 @@ The last step is to link to our new pages from the index page.
 Return to `src/pages/index.js` and let's query for our Markdown slugs and create
 links.
 
-```jsx{3,18-19,29,46-48}
+```jsx{3,18-19,29,47-49}
 import React from "react";
 import g from "glamorous";
 import Link from "gatsby-link";