Add there "exercises" key to config.json
Add there "exercises" key to config.json

First step in transitioning from "problems" to "exercises".

Part of exercism/xjava#125.

FridaTveit/xjava,FridaTveit/xjava,exercism/xjava,jtigger/xjava,nickRm/xjava,jtigger/xjava,jmluy/xjava,nickRm/xjava,jmluy/xjava,exercism/xjava