Merge pull request #587 from exercism/546-fix

luhn: update starter implementation

exercises/luhn/src/main/java/LuhnValidator.java

@@ -0,0 +1,7 @@
+final class LuhnValidator {
+
+    boolean isValid(String candidate) {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+
+}