Fix compilation in RoutingNode

This commit fixes compilation in RoutingNode.java after a backport
brought back usage of an API not available in JDK 8.

server/src/main/java/org/elasticsearch/cluster/routing/RoutingNode.java

@@ -293,7 +293,7 @@ public class RoutingNode implements Iterable<ShardRouting> {
         if (shardRoutings == null) {
             return 0;
         } else {
-            return Math.toIntExact(shardRoutings.stream().filter(Predicate.not(ShardRouting::relocating)).count());
+            return Math.toIntExact(shardRoutings.stream().filter(sr -> sr.relocating() == false).count());
         }
     }