Update versions.properties for building 2.11.2

parser combinators: current tag
https://github.com/scala/scala-parser-combinators/releases

akka: current release http://akka.io/downloads/

scalacheck: current tag
https://github.com/rickynils/scalacheck/releases

Review by @adriaanm.

With this change, I can push a tag and run the [release job](https://scala-webapps.epfl.ch/jenkins/view/scala-release-2.11.x/job/scala-release-2.11.x/build) with the default parameters.