replace unicode arrows

* ⇒, →, ←
* because we don't want to show them in documentation snippets and
  then it's complicated to avoid that when snippets are
  located in src/test/scala in individual modules
* dont replace object `→` in FSM.scala and PersistentFSM.scala

akka-distributed-data/src/test/scala/akka/cluster/ddata/LocalConcurrencySpec.scala

@@ -30,7 +30,7 @@ object LocalConcurrencySpec {
     val replicator = DistributedData(context.system).replicator
 
     def receive = {
-      case s: String ⇒
+      case s: String =>
         val update = Replicator.Update(Updater.key, ORSet.empty[String], Replicator.WriteLocal)(_ :+ s)
         replicator ! update
     }
@@ -64,7 +64,7 @@ class LocalConcurrencySpec(_system: ActorSystem) extends TestKit(_system)
       val updater2 = system.actorOf(Props[Updater], "updater2")
 
       val numMessages = 100
-      for (n ← 1 to numMessages) {
+      for (n <- 1 to numMessages) {
         updater1 ! s"a$n"
         updater2 ! s"b$n"
       }