gdax-java project rename to coinbasepro-java

[irufus]

Coinbase has fully embraced calling the new platform Coinbase Pro. The update is just to align with those changes

[robevansuk]

I think when we get to a point of stability (or even now), the codebase should be duplicated to irufus/coinbase-pro-java and we should contact whoever maintains the documentation at coinbase to make an update to the URL in their docs. I've connected with several engineers at coinbase via linkedin and will suggest this once I find out who to contact