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/cookbook/RecipeWorkerPool.scala

@@ -25,11 +25,11 @@ class RecipeWorkerPool extends RecipeSpec {
       def balancer[In, Out](worker: Flow[In, Out, Any], workerCount: Int): Flow[In, Out, NotUsed] = {
         import GraphDSL.Implicits._
 
-        Flow.fromGraph(GraphDSL.create() { implicit b ⇒
+        Flow.fromGraph(GraphDSL.create() { implicit b =>
           val balancer = b.add(Balance[In](workerCount, waitForAllDownstreams = true))
           val merge = b.add(Merge[Out](workerCount))
 
-          for (_ ← 1 to workerCount) {
+          for (_ <- 1 to workerCount) {
             // for each worker, add an edge from the balancer to the worker, then wire
             // it to the merge element
             balancer ~> worker.async ~> merge