fix compile error

Author: yangjiandan

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/test/java/org/apache/hadoop/mapreduce/v2/app/TestTaskHeartbeatHandler.java

@@ -38,7 +38,7 @@
 import org.apache.hadoop.yarn.api.records.ApplicationId;
 import org.apache.hadoop.yarn.event.Event;
 import org.apache.hadoop.yarn.event.EventHandler;
-import org.apache.hadoop.yarn.util.Clock;
+import org.apache.hadoop.util.Clock;
 import org.apache.hadoop.yarn.util.ControlledClock;
 import org.apache.hadoop.util.SystemClock;
 import org.junit.jupiter.api.Test;