It changed React Playground to add a required props but unfortunately didn't update the call sites of the front-page. I don't think it should be required so I'm just making it optional and providing the correct default value.
Test Plan:
- Open the front page and make sure examples are working
- Open /react/jsx-compiler.html and make sure it is working
- Open /react/html-jsx.html and make sure it is working
Remember that one time I wrote release notes and said:
> This is a breaking change - if you were using class, you must change
> this to className or your components will be visually broken.
Good thing I didn't listen to myself!
