Fix JsonToStringStyleTest.NestingPerson javadoc (closes #243)

A {@link} javadoc can only reference a resolvable class name. The
{@link} tag in NestingPerson's javadoc is thus broken, as it directly
references JsonToStringStyle without qualifying it with the enclosing
ToStringStyle class.

This patch adds the enclosing class to the javadoc, thus "unbreaking"
the reference.

src/test/java/org/apache/commons/lang3/builder/JsonToStringStyleTest.java

@@ -359,7 +359,7 @@ public class JsonToStringStyleTest {
     }
     
     /**
-     * An object with nested object structures used to test {@link JsonToStringStyle}.
+     * An object with nested object structures used to test {@link ToStringStyle.JsonToStringStyle}.
      * 
      */
     static class NestingPerson {