Depend on futures-util instead of futures

docs/COMPARISONS.md

@@ -19,7 +19,7 @@ let dag = DagRunner::new();
 let x = dag.add_task(Value(2));
 let y = dag.add_task(Value(3));
 let sum = dag.add_task(Add).depends_on((x, y));
-dag.run(|fut| tokio::spawn(fut).map(Result::unwrap)).await?;
+dag.run(|fut| async move { tokio::spawn(fut).await.unwrap() }).await?;
 ```
 
 **dagrs** (Complex: traits + channels + IDs + manual wiring):