Update the Cookbook for Java page #1228

https://www.rethinkdb.com/docs/cookbook/java/

The cookbook for Java is showing the Javascript functions. There is a note that the Cookbook will be updated after the offical Java driver is released. It seems the driver has been stable for the past 11 months. Maybe that makes it a good time for the Cookbook to be updated?

I'm still just learning Java, but I can help out with the documentation if you're looking for help from the community.

Thank you!