fixed compile errors due upstream change

Original commit: elastic/x-pack-elasticsearch@0a9d73d2be

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/action/InternalStartDatafeedAction.java

@@ -83,6 +83,11 @@ public class InternalStartDatafeedAction extends
             this.holder = holder;
         }
 
+        @Override
+        public boolean shouldCancelChildrenOnCancellation() {
+            return true;
+        }
+
         @Override
         protected void onCancelled() {
             stop();

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/action/PostDataAction.java

@@ -138,6 +138,10 @@ public class PostDataAction extends Action<PostDataAction.Request, PostDataActio
             super(id, type, action, jobId + "_post_data", parentTaskId);
         }
 
+        @Override
+        public boolean shouldCancelChildrenOnCancellation() {
+            return true;
+        }
     }
 
     public static class Request extends ActionRequest {