Set JDiff stable to 0.20.2

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@917674 13f79535-47bb-0310-9956-ffa450edef68

build.xml

@@ -114,7 +114,7 @@
 
   <property name="jdiff.build.dir" value="${build.docs}/jdiff"/>
   <property name="jdiff.xml.dir" value="${lib.dir}/jdiff"/>
-  <property name="jdiff.stable" value="0.20.1"/>
+  <property name="jdiff.stable" value="0.20.2"/>
   <property name="jdiff.stable.javadoc" 
             value="http://hadoop.apache.org/core/docs/r${jdiff.stable}/api/"/>