Issue with Wizard Form Sandbox

### Are you submitting a **bug report** or a **feature request**?

### What is the current behavior?

The sandbox for your wizard form is missing a dependency so it doesnt render.
Getting the error - Could not find dependency: 'prop-types' relative to '/Wizard.js'
https://codesandbox.io/s/github/final-form/react-final-form/tree/master/examples/wizard?from-embed