Only add `: Unit =` to procedure style method def to mute warning in scala 2.11
+ Change nothing in code but update play-json (optional dependency) to 2.3.0-RC1 & akka-actor 2.3.2
+ cross compile for scala 2.11 & scala 2.10
+ Also update sbt 0.13.5-RC1
+ Bump v3.1.0