remove final from class declaration in scrabble-score exercise

exercises/scrabble-score/src/main/java/Scrabble.java

@@ -1,4 +1,4 @@
-final class Scrabble {
+class Scrabble {
 
     Scrabble(String word) {
         throw new UnsupportedOperationException("Delete this statement and write your own implementation.");