add scalacOptions for Scala.js source map
add scalacOptions for Scala.js source map

https://github.com/scala-js/scala-js/blob/v0.6.8/compiler/src/main/scala/org/scalajs/core/compiler/ScalaJSPlugin.scala#L147-L151

scalapb/ScalaPB,scalapb/ScalaPB,scalapb/ScalaPB,dotty-staging/ScalaPB,trueaccord/ScalaPB,scalapb/ScalaPB