code: def get_series_vintage_dates(self, series_id):
          
          url = "%s/series/vintagedates?series_id=%s" % (self.root_url, series_id)
          root = self.__fetch_data(url)
          if root is None:
              raise ValueError('No vintage date exists for series id: ' + series_id)
          dates = []
          for child in root.getchildren():
              dates.append(self._parse(child.text))
          return dates
docs: Get a list of vintage dates for a series. Vintage dates are the dates in history when a
          series' data values were revised or new data values were released.
  
          Parameters
          ----------
          series_id : str
              Fred series id such as 'CPIAUCSL'
  
          Returns
          -------
          dates : list
              list of vintage dates