title: How can in run a dag with one task
body: <pre><code>default_args = {
  "owner": "airflow_admin",
  "start_date": datetime(2017, 8, 29),
  "schedule_interval":'*/5 * * * *'
   }
  with DAG(
  'my_first_dag',
  catchup=False,
  default_args=default_args,
  ) as dag:
  
     task1 = BashOperator(
     task_id='id1',
     bash_command=bash_.format('db1', 'tab1'))
  
  task1
  </code></pre>
  
  <p>does anyone knows how to launch a dag with one task please, the code above don't work, the dag is launched properly</p>