Move WDS reference set files under folder

src/main/java/org/moeaframework/benchmarks/BenchmarkProvider.java

@@ -23,7 +23,7 @@ public BenchmarkProvider() {
 		register("LakeProblem", () -> new LakeProblem(), "./pf/LakeProblem.reference");
 
 		for (WDSInstance variant : WDSInstance.values()) {
-			register("WDS(" + variant.getName() + ")", () -> new WDS(variant), "./pf/" + variant.getName() + ".reference");
+			register("WDS(" + variant.getName() + ")", () -> new WDS(variant), "./pf/WDS/" + variant.getName() + ".reference");
 		}
 	}