Play 2.5 with Akka - could not find implicit value for parameter timeout: akka.util.Timeout

I'm attempting to test out Akka with Play 2.5 and I'm running into a compile error I can't seem to get around.

I'm following this page from the Play docs: https://playframework.com/documentation/2.5.x/ScalaAkka

Here is the full code:

package controllers

import javax.inject.{Inject, Singleton}
import akka.actor.ActorSystem
import controllers.HelloActor.SayHello
import play.api.mvc._
import play.api.libs.concurrent.Execution.Implicits.defaultContext
import scala.concurrent.duration._
import akka.pattern.ask

@Singleton
class Application @Inject()(system: ActorSystem) extends Controller {

  implicit val timeout = 5.seconds

  val helloActor = system.actorOf(HelloActor.props, "hello-actor")

  def sayHello(name: String) = Action.async {
    (helloActor ? SayHello(name)).mapTo[String].map { message =>
      Ok(message)
    }
  }
}

import akka.actor._

object HelloActor {
  def props = Props[HelloActor]

  case class SayHello(name: String)

}

class HelloActor extends Actor {
  import HelloActor._

  def receive = {
    case SayHello(name: String) =>
      sender() ! "Hello, " + name
  }
}

My route looks like:

GET     /:name                      controllers.Application.sayHello(name: String)

And, finally, my build.sbt:

name := "AkkaTest"

version := "1.0"

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

scalaVersion := "2.11.7"

libraryDependencies ++= Seq( jdbc , cache , ws   , specs2 % Test )

unmanagedResourceDirectories in Test <+=  baseDirectory ( _ /"target/web/public/test" )  

resolvers += "scalaz-bintray" at "https://dl.bintray.com/scalaz/releases"

routesGenerator := InjectedRoutesGenerator

When I attempt to run this, I get the following compilation error:

could not find implicit value for parameter timeout: akka.util.Timeout

I've tried moving around the timeout to no avail. Does anyone have an idea what might cause this compilation error?