title: How to convert Timestamp to DateTime from firebase with flutter
body: <p>I have Timestamp item in firebase. I get the item from dart code timestamp type.
  It shows like 'Timestamp(seconds=1590903768, nanoseconds=26999000)' as it is.</p>
  
  <p>I would like to show on my Application only Date like '2020-06-01' or '06-01'.</p>
  
  <p>Please give me advice.</p>