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/GSetSpec.scala

@@ -140,7 +140,7 @@ class GSetSpec extends WordSpec with Matchers {
       val GSet(elements1) = s1
       val elements2: Set[String] = elements1
       Changed(GSetKey[String]("key"))(s1) match {
-        case c @ Changed(GSetKey("key")) ⇒
+        case c @ Changed(GSetKey("key")) =>
           val GSet(elements3) = c.dataValue
           val elements4: Set[String] = elements3
           elements4 should be(Set("a", "b"))