Amend HFDS-3955. Forgot an import of ImmutableList in previous patch.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-3077@1387740 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/Journal.java

@@ -58,6 +58,7 @@ import org.apache.hadoop.security.SecurityUtil;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.base.Stopwatch;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Range;
 import com.google.common.collect.Ranges;
 import com.google.protobuf.TextFormat;