Bumped version to 3.0.0-M6.
Bumped version to 3.0.0-M6.

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