squash some warnings

akka-stream-tests/src/test/java/akka/stream/javadsl/SourceTest.java

@@ -450,6 +450,7 @@ public class SourceTest extends StreamTest {
     final JavaTestKit probe = new JavaTestKit(system);
     Source<String, Cancellable> tickSource = Source.tick(FiniteDuration.create(1, TimeUnit.SECONDS),
         FiniteDuration.create(500, TimeUnit.MILLISECONDS), "tick");
+    @SuppressWarnings("unused")
     Cancellable cancellable = tickSource.to(Sink.foreach(new Procedure<String>() {
       public void apply(String elem) {
         probe.getRef().tell(elem, ActorRef.noSender());