Guide should mention sbt 0.13.5 as a minimum requirement

I setup build.sbt like this:
```
name := "my-first-app"

version := "1.0.0-SNAPSHOT"

lazy val root = (project in file(".")).enablePlugins(PlayScala)
```

as per [this guide](http://www.playframework.com/documentation/2.3.x/NewApplication)

But it throws this exception:
```
build.sbt:5: error: value enablePlugins is not a member of sbt.Project
lazy val root = (project in file(".")).enablePlugins(PlayScala)
                                       ^
sbt.compiler.EvalException: Type error in expression
	at sbt.compiler.Eval.checkError(Eval.scala:343)
	at sbt.compiler.Eval.compileAndLoad(Eval.scala:165)
	at sbt.compiler.Eval.evalCommon(Eval.scala:135)
	at sbt.compiler.Eval.evalDefinitions(Eval.scala:109)
	at sbt.EvaluateConfigurations$.evaluateDefinitions(EvaluateConfigurations.scala:125)
	at sbt.EvaluateConfigurations$.evaluateSbtFile(EvaluateConfigurations.scala:48)
	at sbt.Load$.sbt$Load$$loadSettingsFile$1(Load.scala:502)
	at sbt.Load$$anonfun$sbt$Load$$memoLoadSettingsFile$1$1.apply(Load.scala:497)
	at sbt.Load$$anonfun$sbt$Load$$memoLoadSettingsFile$1$1.apply(Load.scala:496)
	at scala.Option.getOrElse(Option.scala:120)
	at sbt.Load$.sbt$Load$$memoLoadSettingsFile$1(Load.scala:496)
	at sbt.Load$$anonfun$loadSettings$1$2.apply(Load.scala:495)
	at sbt.Load$$anonfun$loadSettings$1$2.apply(Load.scala:495)
	at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
	at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
	at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
	at scala.collection.AbstractTraversable.map(Traversable.scala:105)
	at sbt.Load$.loadSettings$1(Load.scala:495)
	at sbt.Load$.sbt$Load$$expand$1(Load.scala:508)
	at sbt.Load$.loadSettings(Load.scala:512)
	at sbt.Load$.sbt$Load$$loadSbtFiles$1(Load.scala:466)
	at sbt.Load$.defaultLoad$1(Load.scala:472)
	at sbt.Load$.loadTransitive(Load.scala:475)
	at sbt.Load$.loadProjects$1(Load.scala:421)
	at sbt.Load$.loadUnit(Load.scala:422)
	at sbt.Load$$anonfun$15$$anonfun$apply$11.apply(Load.scala:258)
	at sbt.Load$$anonfun$15$$anonfun$apply$11.apply(Load.scala:258)
	at sbt.BuildLoader$$anonfun$componentLoader$1$$anonfun$apply$4$$anonfun$apply$5$$anonfun$apply$6.apply(BuildLoader.scala:93)
	at sbt.BuildLoader$$anonfun$componentLoader$1$$anonfun$apply$4$$anonfun$apply$5$$anonfun$apply$6.apply(BuildLoader.scala:92)
	at sbt.BuildLoader.apply(BuildLoader.scala:143)
	at sbt.Load$.loadAll(Load.scala:314)
	at sbt.Load$.loadURI(Load.scala:266)
	at sbt.Load$.load(Load.scala:262)
	at sbt.Load$.load(Load.scala:253)
	at sbt.Load$.apply(Load.scala:137)
	at sbt.Load$.defaultLoad(Load.scala:40)
	at sbt.BuiltinCommands$.doLoadProject(Main.scala:458)
	at sbt.BuiltinCommands$$anonfun$loadProjectImpl$2.apply(Main.scala:452)
	at sbt.BuiltinCommands$$anonfun$loadProjectImpl$2.apply(Main.scala:452)
	at sbt.Command$$anonfun$applyEffect$1$$anonfun$apply$2.apply(Command.scala:60)
	at sbt.Command$$anonfun$applyEffect$1$$anonfun$apply$2.apply(Command.scala:60)
	at sbt.Command$$anonfun$applyEffect$2$$anonfun$apply$3.apply(Command.scala:62)
	at sbt.Command$$anonfun$applyEffect$2$$anonfun$apply$3.apply(Command.scala:62)
	at sbt.Command$.process(Command.scala:95)
	at sbt.MainLoop$$anonfun$1$$anonfun$apply$1.apply(MainLoop.scala:100)
	at sbt.MainLoop$$anonfun$1$$anonfun$apply$1.apply(MainLoop.scala:100)
	at sbt.State$$anon$1.process(State.scala:179)
	at sbt.MainLoop$$anonfun$1.apply(MainLoop.scala:100)
	at sbt.MainLoop$$anonfun$1.apply(MainLoop.scala:100)
	at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:18)
	at sbt.MainLoop$.next(MainLoop.scala:100)
	at sbt.MainLoop$.run(MainLoop.scala:93)
	at sbt.MainLoop$$anonfun$runWithNewLog$1.apply(MainLoop.scala:71)
	at sbt.MainLoop$$anonfun$runWithNewLog$1.apply(MainLoop.scala:66)
	at sbt.Using.apply(Using.scala:25)
	at sbt.MainLoop$.runWithNewLog(MainLoop.scala:66)
	at sbt.MainLoop$.runAndClearLast(MainLoop.scala:49)
	at sbt.MainLoop$.runLoggedLoop(MainLoop.scala:33)
	at sbt.MainLoop$.runLogged(MainLoop.scala:25)
	at sbt.StandardMain$.runManaged(Main.scala:57)
	at sbt.xMain.run(Main.scala:29)
	at xsbt.boot.Launch$$anonfun$run$1.apply(Launch.scala:109)
	at xsbt.boot.Launch$.withContextLoader(Launch.scala:129)
	at xsbt.boot.Launch$.run(Launch.scala:109)
	at xsbt.boot.Launch$$anonfun$apply$1.apply(Launch.scala:36)
	at xsbt.boot.Launch$.launch(Launch.scala:117)
	at xsbt.boot.Launch$.apply(Launch.scala:19)
	at xsbt.boot.Boot$.runImpl(Boot.scala:44)
	at xsbt.boot.Boot$.main(Boot.scala:20)
	at xsbt.boot.Boot.main(Boot.scala)
[error] sbt.compiler.EvalException: Type error in expression

```