renderprops Transition notification demo issues

[daynekilheffer]

I've noticed a few issues with the Transition's notification example for renderprops.

1. The source link sends you to a 404 page. I believe the link field for renderprops/messages in examples-renderprops.js is simply pointing to the wrong location ("notifications" vs "messages")
2. the example doesn't seem to be working as expected. While clicking on the demo body creates new messages, they do not animate. Locally removing the native prop works, but I don't know the inner workings of this library to know why that is the case, so I don't feel comfortable creating a PR.