Rocket emoji not showing in header

[allisonwhilden]

Minor issue. Just noticed that the rocket ship emoji is not displaying correctly in the header in the overview of Chapter 1. All you get is :rocket:.

I don't know if the markdown supports emoji in headers or if something else is going on.

[allisonwhilden]

Looks like this is fixed by #85. I will close this issue as there is already a PR for it.