Set jdiff.stable.api to 2.8.0

(cherry picked from commit e7b7c96a30b0fee3af22a7719eaaa6481e76a963)

hadoop-project-dist/pom.xml

@@ -145,7 +145,7 @@
         <activeByDefault>false</activeByDefault>
       </activation>
       <properties>
-        <jdiff.stable.api>2.7.2</jdiff.stable.api>
+        <jdiff.stable.api>2.8.0</jdiff.stable.api>
         <jdiff.stability>-unstable</jdiff.stability>
         <!-- Commented out for HADOOP-11776 -->
         <!-- Uncomment param name="${jdiff.compatibility}" in javadoc doclet if compatibility is not empty -->