Pass 2.11, rather than 2.11.0, as scala.binary.version

To remedy the errors:

    Unable to resolve artifact: Missing:
    ----------
    1) org.scala-lang.modules:scala-partest_2.11.0:jar:1.0.0

in:

  https://scala-webapps.epfl.ch/jenkins/view/scala-release-2.11.x/job/scala-release-2.11.x/55