Bump up sbt version to 0.13.9.
Bump up sbt version to 0.13.9.

cheeseng/scalatest,dotty-staging/scalatest,cheeseng/scalatest,scalatest/scalatest,scalatest/scalatest,scalatest/scalatest,dotty-staging/scalatest,cheeseng/scalatest,dotty-staging/scalatest