Pin javac target compatibility version

[mroth]

Essentially we need this, to help insulate this project from particulars of the local develop environment during compilation:

javacOptions ++= Seq("-source", "1.8", "-target", "1.8")

With the format of the build.sbt for this particular project I couldn't figure out where to put it, so figured it was easier to just make an issue for you on this one project @adridadou. :-)

(As you noticed, it appears all the java-specific versions already have this pragma by default, so its just the Scala ones that need it added.)