All works well with Play 2.2.1. However, when upgrading to Play 2.2.2 and deploying to Heroku, process warns about:
sbt.ResolveException: unresolved dependency:
Ok so I managed to do the trick by adding this line, before my series of resolvers +=:
resolvers +=
resolvers := Seq("typesafe" at "http://repo.typesafe.com/typesafe/releases/")
If it can help some people coming across the same issue :)