title: String to Date conversion in wrangler
body: <p>I am having my raw data in the format of '2019-10-10' in csv file.
  After reading file I have loaded into Wrangler for transformation .
  My target column is having data type as DATE.</p>
  
  <p>I have applied below transformation:
  set-column TODATE TODATE=UNIX_DATE('2019-10-10')</p>
  
  <p>Here UNIX_DATE('2019-10-10') will convert date into Unix time stamp and post that Wrangler will take care while dumping into to Target table.</p>
  
  <p>Here it is giving error like </p>
  
  <p>Pipeline faile: jexl transformation wrong.</p>
  
  <p>Expected result should be in 2019-10-10 format in target table.
  Please help further.</p>