Merge pull request #556 from exercism/533-hello-world-starter

hello-world: standardize starter implementation

exercises/hello-world/src/main/java/HelloWorld.java

@@ -1,5 +1,5 @@
 public class HelloWorld {
     public static String hello(String name) {
-        return null;
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
     }
 }