removed the static qualifier for inner class NaturalComparator,

the class *really* should be static, but this triggers a bug in the clirr plugin

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@611501 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/math/stat/Frequency.java

@@ -435,7 +435,7 @@ public class Frequency implements Serializable {
      * A Comparator that compares comparable objects using the
      * natural order.  Copied from Commons Collections ComparableComparator.
      */
-    private static class NaturalComparator implements Comparator, Serializable {
+    private class NaturalComparator implements Comparator, Serializable {
         private static final long serialVersionUID = -3852193713161395148L;
 
         /**