Update sbt-dotty to 0.4.0

Author: scala-steward

project/plugins.sbt

@@ -4,4 +4,4 @@ val scalaJSVersion =
 addSbtPlugin("org.scala-lang.modules" % "sbt-scala-module" % "2.1.3")
 addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "0.6.1")
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % scalaJSVersion)
-addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.3.4")
+addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.4.0")