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-docs/src/test/scala/docs/stream/RestartDocSpec.scala

@@ -40,7 +40,7 @@ class RestartDocSpec extends AkkaSpec with CompileOnlySpec {
         maxBackoff = 30.seconds,
         randomFactor = 0.2, // adds 20% "noise" to vary the intervals slightly
         maxRestarts = 20 // limits the amount of restarts to 20
-      ) { () ⇒
+      ) { () =>
         // Create a source from a future of a source
         Source.fromFutureSource {
           // Make a single request with akka-http
@@ -56,7 +56,7 @@ class RestartDocSpec extends AkkaSpec with CompileOnlySpec {
       //#with-kill-switch
       val killSwitch = restartSource
         .viaMat(KillSwitches.single)(Keep.right)
-        .toMat(Sink.foreach(event ⇒ println(s"Got event: $event")))(Keep.left)
+        .toMat(Sink.foreach(event => println(s"Got event: $event")))(Keep.left)
         .run()
 
       doSomethingElse()