title: is there any way to calculate date in airflow?
body: <p>i create a Dag that will be scheduled to run every day once a day - the dag wont get any parameters . each day the dag ran i need to calculate yesterdays date (current Date -1)  and pass it for all the operators in the dag (same date). 
  i saw that i can use Airflow-macros to compute the date , but the problem is ,the operator i use in t2 (must use this operator and cant change it) pass the data to the dictionary (default_param_dict) as a string and don't compute the macro.</p>
  
  <p>is there any other way to compute the date without macros? using X-com is not relevant because i can only use the operators and cant change their code.</p>
  
  <p>need you help:)</p>
  
  <p>adding my dag example:</p>
  
  <pre class="lang-py prettyprint-override"><code>t1 = SimpleHttpOperator(
      task_id='check_if_daily_report_ready',
      method='GET',
      endpoint="/bla/bla?date={date}".format(
          date='{{ (execution_date - macros.timedelta(days=1)).strftime("%Y-%m-%d") }}'),
      http_conn_id="conn1",
      headers={"Content-Type": "application/json"},
      response_check=lambda response: True if response.status_code == 200 else False,
      dag=dag,
  )
  
  
  
  t2 = Queryperator(
      task_id='cal',
      query_file='ca.sql',
      query_folder='include/sql_files/bla',
      token='Token',
      default_param_dict={"date": '{{ (execution_date - macros.timedelta(days=1)).strftime("%Y-%m-%d") }}'},
      dag=dag
  )
  </code></pre>