Merge pull request #26391 from akka/wip-26382-patriknw

fix 2.13 compilation error, SortedSet, #26382

.travis.yml

@@ -5,6 +5,7 @@ sudo: false
 scala:
   - "2.12.8"
   - "2.11.12"
+  - "2.13.0-M5"
 
 before_install:
   # using jabba for custom jdk management

akka-cluster-tools/src/multi-jvm/scala/akka/cluster/singleton/ClusterSingletonManagerDownedSpec.scala

@@ -87,7 +87,7 @@ class ClusterSingletonManagerDownedSpec extends MultiNodeSpec(ClusterSingletonMa
       within(15.seconds) {
         awaitAssert {
           cluster.state.members.size should ===(3)
-          cluster.state.members.map(_.status) should ===(Set(MemberStatus.Up))
+          cluster.state.members.unsorted.map(_.status) should ===(Set(MemberStatus.Up))
         }
       }
       runOn(first) {