upgrade to sbt 1?

sbt-scala-module is now published for sbt 1, so modules are free to upgrade. doing so is as easy as e.g. https://github.com/scala/scala-swing/pull/93

but it requires dropping support for Java 6, which we probably shouldn't do without signaling it in the version number

@ashawley I can't recall if we've discussed this before for this module. hard to keep all the modules straight in my head