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-cluster/src/multi-jvm/scala/akka/cluster/AttemptSysMsgRedeliverySpec.scala

@@ -27,7 +27,7 @@ object AttemptSysMsgRedeliveryMultiJvmSpec extends MultiNodeConfig {
 
   class Echo extends Actor {
     def receive = {
-      case m ⇒ sender ! m
+      case m => sender ! m
     }
   }
 }