Code cleanup

strategy/src/test/java/com/iluwatar/strategy/DragonSlayingStrategyTest.java

@@ -91,7 +91,7 @@ public class DragonSlayingStrategyTest {
   }
 
   private class InMemoryAppender extends AppenderBase<ILoggingEvent> {
-    private List<ILoggingEvent> log = new LinkedList<>();
+    private final List<ILoggingEvent> log = new LinkedList<>();
 
     public InMemoryAppender() {
       ((Logger) LoggerFactory.getLogger("root")).addAppender(this);