Switched the PHP example

I'm a bit biased as I work for the company which did it, but I wanted to send this PR to at least check what criteria you guys use for picking the examples. This library supports a few more things and it's [decently followed](https://packagist.org/packages/namshi/jose) (18k installations), etc etc

Let me know :) No problem if you guys wanna keep the firebase example!

Cheers,