=act Make SerializationCompatibilitySpec pass on Scala 2.11.x

* The serailization format of Option has changed between Scala 2.10.x and 2.11.x
Merge pull request #15815 from akka/wip-15807-make-SerializationCompatibilitySpec-pass-on-scala-2.11.x-master-ban

(Validation Only) =act Make SerializationCompatibilitySpec pass on Scala 2.11.x