message: [cache] Fixing json.dumps for timestamp
diff: @@ -289,7 +289,7 @@ class BaseViz(object):
  self.status != utils.QueryStatus.FAILED):
  cached_dttm = datetime.utcnow().isoformat().split('.')[0]
  try:
  - cache_value = json.dumps({
  + cache_value = self.json_dumps({
  'data': data,
  'dttm': cached_dttm,
  })
  