为什么在build.sbt工作时,sbt报告“没有找到：Build PlayScala”

<root>
----build.sbt
----project
    ----Build.scala
    ----plugins.sbt
----common
----LoggingModule

LoggingModule是一个Play Framework项目,而普通的是一个简单的Scala项目.

在plugins.sbt中：

resolvers += "Typesafe repo" at "http://repo.typesafe.com/typesafe/releases/"

addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.3.3")

虽然我在build.sbt中有这些,但一切正常,它识别了PlayScala：

name := "Multi-Build"

lazy val root = project.in(file(".")).aggregate(common,LoggingModule).dependsOn(common,LoggingModule)

lazy val common = project in file("common")

lazy val LoggingModule = (project in file("LoggingModule")).enablePlugins(PlayScala)

但是,一旦我把它放在项目/ Build.scala而不是`build.sbt’中,如下所示：

object RootBuild extends Build {  

  lazy val root = project.in(file("."))
    .aggregate(common,LoggingModule)
    .dependsOn(common,LoggingModule)

  lazy val common = project in file("common")
  lazy val LoggingModule = (project in file("LoggingModule")).enablePlugins(PlayScala)

  ...//other settings
}

它会产生错误：

not found: value PlayScala
lazy val LoggingModule = (project in file("LoggingModule")).enablePlugins(PlayScala)
                                                                          ^

如何解决问题？