Update the sbt, spray and akka to current releases

This is just an update to the sbt, spray and akka versions to the current releases, to avoid the binary incompatibility between 2.2 and 2.3 of akka versions, described here:
https://groups.google.com/forum/#!msg/play-framework-dev/ovz9kLaYpOE/--SxQuEYuWcJ