Why Scala playframework doesn't import library

I'm trying to use this tutorial. But I got stuck while trying to import library import org.scalatestplus.play._

I added this dependency in my build.sbt

  libraryDependencies += "org.scalatestplus" % "play_2.10" % "1.2.0"

It doesn't update dependency list.

If I try activator update I succeed as

$ activator update

[info] Loading project definition from /Users/masum/work/app/project
[info] Set current project to app (in build file:/Users/masum/work/app/)
[info] Updating {http://file:/Users/masum/work/app/}root...
[info] Resolving jline#jline;2.12 ...
[info] downloading http://ift.tt/1DPyjNN ...
  [info]    [SUCCESSFUL ] org.scalatestplus#play_2.11;1.2.0!play_2.11.jar (1253ms)
  [info] Done updating.
  [success] Total time: 6 s, completed Mar 3, 2015 5:50:21 PM

Even after that I can't

   import org.scalatestplus.play._

Here is my build.sbt:-

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

  scalaVersion := "2.11.5"

  libraryDependencies += "org.scalatestplus" % "play_2.11" % "1.2.0" % "test"

 libraryDependencies ++= Seq(
 jdbc,
 anorm,
 cache,
 ws,
 "com.typesafe.slick" % "slick_2.11" % "3.0.0-M1",
 "com.typesafe.play" % "play-slick_2.11" % "0.8.1",
 "org.slf4j" % "slf4j-nop" % "1.6.4",
 "org.postgresql" % "postgresql" % "9.4-1200-jdbc41",
 "org.scalatest" % "scalatest_2.11" % "2.2.4" % "test",
 "org.mockito" % "mockito-core" % "1.10.19" % "test",
 "com.h2database" % "h2" % "1.3.166",
 "org.xerial" % "sqlite-jdbc" % "3.6.20",
 "org.scala-lang" % "scala-actors" % "2.11.0"
 )

What is wrong? How to import org.scalatestplus.play._