Update React tutorial link (#3141)

The proposed changes replace the link - `https://facebook.github.io/react/tutorial/tutorial.html` (which is an old link) with `https://reactjs.org/tutorial/tutorial.html` (which is the updated the link).

docs/docs/building-with-components.md

@@ -6,7 +6,7 @@ title: Building with Components
 
 To use Gatsby, you will need a basic understanding of React components.
 
-The [official tutorial](https://facebook.github.io/react/tutorial/tutorial.html)
+The [official tutorial](https://reactjs.org/tutorial/tutorial.html)
 is a good place to start.
 
 ## Why React components?