Gatsby: [docs] Align code in StaticQuery video and written tutorial

[jlengstorf]

Right now, the example code in the StaticQuery docs isn't aligned between the video and the written docs.

To avoid confusion, we should probably update the written docs to use the same example as the video.

The code used in the video is here: https://github.com/jlengstorf/gatsby-staticquery

This would be a great first contribution for someone! 💪💜

[nhc]

So I had a go at the above issue.