HDFS-6107: fix comment (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1578511 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestFsDatasetCache.java

@@ -546,7 +546,7 @@ public class TestFsDatasetCache {
         MetricsAsserts.getLongCounter("BlocksCached", dnMetrics));
     
     // Uncache the big file and verify that the small file can now be
-    // cached (regression test for HDFS-XXXX)
+    // cached (regression test for HDFS-6107)
     dfs.removeCacheDirective(bigCacheDirectiveId);
     GenericTestUtils.waitFor(new Supplier<Boolean>() {
       @Override