fix return type hint in write_dag

ezdag/dags.py

@@ -164,7 +164,7 @@ def write_dag(
     dag_dir: Path = Path.cwd(),
     formatter: Optional[dags.NodeNameFormatter] = None,
     **kwargs,
-) -> None:
+) -> Path:
     """Write out the given DAG to the given directory.
 
     This includes the DAG description file itself, as well as any associated