Address soundness hole in cycle prevention

examples/04_parallel_computation.rs

@@ -123,9 +123,7 @@ async fn main() -> DagResult<()> {
         let sum3 = dag.add_task(ComputeSum::new(501, 751, WORK_DELAY));
         let sum4 = dag.add_task(ComputeSum::new(751, 1001, WORK_DELAY));
 
-        let total = dag
-            .add_task(Aggregate)
-            .depends_on((&sum1, &sum2, &sum3, &sum4));
+        let total = dag.add_task(Aggregate).depends_on((sum1, sum2, sum3, sum4));
 
         dag.run(|fut| tokio::spawn(fut).map(Result::unwrap)).await?;