Fix linter warning.

Author: aardvark179

src/main/java/org/truffleruby/core/MarkingService.java

@@ -84,7 +84,7 @@ public ReferenceProcessingService<MarkerReference> service() {
     private final ThreadLocal<Deque<ArrayList<Object>>> stackPreservation = ThreadLocal.withInitial(() -> new ArrayDeque<>());
 
     private Object[] keptObjects;
-    private final ArrayDeque<Object[]> oldKeptObjects = new ArrayDeque<Object[]>();
+    private final ArrayDeque<Object[]> oldKeptObjects = new ArrayDeque<>();
 
     private int counter = 0;