changed build.sbt to work with play 2.3

Hy Pascal

This seems to work for me. 

After modifying `build.sbt`, I run `sbt reload`,`sbt compile`,`sbt package` and copied the generated `play-json-zipper_2.11-1.1.jar` to the `libs` folder in my project... 

Please write me, when you upload the modified project to bintray, so I can replace `play-json-zipper_2.11-1.1.jar` with your managed dependency... 
Upgrading specs2 to version 2 breaks the tests: "JsZipperMSpec.scala:300: could not find implicit value for evidence parameter of type org.specs2.execute.AsResult[Unit]"