input: Write a python function to validate a given date.
  assert validate_date(2020, 11, 40) == False
  assert validate_date(2021, 2, 29) == False
  assert validate_date(2020, 2, 29) == True
  assert validate_date(2019, 6, 30) == True
output: def validate_date(year, month, day):
      import datetime
      try:
          datetime.datetime(year, month, day)
          return True
      except ValueError:
          return False