Fix Checktyle

Author: garydgregory

src/main/java/org/apache/commons/cli/HelpFormatter.java

@@ -68,7 +68,7 @@ public class HelpFormatter {
     /**
      * This class implements the {@code Comparator} interface for comparing Options.
      */
-    private static class OptionComparator implements Comparator<Option>, Serializable {
+    private static final class OptionComparator implements Comparator<Option>, Serializable {
         /** The serial version UID. */
         private static final long serialVersionUID = 5305467873966684014L;