- fix style 2

Author: K0K0V0K

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/security/authorize/TaskLevelSecurityEnforcer.java

@@ -40,11 +40,11 @@
  * <p>This prevents unauthorized or unsafe custom code from running inside
  * cluster containers.</p>
  */
-public class TaskLevelSecurityEnforcer {
+public final class TaskLevelSecurityEnforcer {
   private static final Logger LOG = LoggerFactory.getLogger(TaskLevelSecurityEnforcer.class);
 
   /**
-   * Default constructor
+   * Default constructor.
    */
   private TaskLevelSecurityEnforcer() {
   }