Update to sbt 0.13.7 and cached resolution

Sbt 0.13.7 was just released:

https://groups.google.com/forum/#!msg/sbt-dev/hSbUnyG3J6k/-130EsIaEu4J

should be totally compatible.

It has a new feature: cached resolution. This makes compilation MUCH faster after the first run. It caches the poms from all the deps so they don't need to be fetched to walk the tree, and it keeps a serialized total view of the dependency graph. This was a huge speedup for me.