Merge pull request #641 from scala-steward/update/play-docs-3.1.0-M4

play-docs, play-docs-sbt-plugin, ... 3.1.0-M4 (was 3.1.0-M3)

Author: mkurz

docs/project/plugins.sbt

@@ -6,7 +6,7 @@ lazy val sbtPlayEbean = ProjectRef(Path.fileProperty("user.dir").getParentFile,
 
 resolvers ++= DefaultOptions.resolvers(snapshot = true)
 
-addSbtPlugin("org.playframework" % "play-docs-sbt-plugin" % sys.props.getOrElse("play.version", "3.1.0-M3"))
+addSbtPlugin("org.playframework" % "play-docs-sbt-plugin" % sys.props.getOrElse("play.version", "3.1.0-M4"))
 
 addSbtPlugin("com.lightbend.sbt" % "sbt-java-formatter" % "0.8.0")