message: fix serialize problem.
diff: @@ -41,7 +41,7 @@ mod duration_second {
  where
  S: Serializer,
  {
  - s.serialize_u64(x.as_millis() as u64)
  + s.serialize_u64(x.as_secs())
  }
  }
  @@ -456,11 +456,12 @@ mod tests {
  #[test]
  fn test_write_token() {
  + let now: DateTime<Utc> = Utc::now();
  let scope: HashSet<String> = HashSet::from_iter("playlist-read-private playlist-read-collaborative playlist-modify-public playlist-modify-private streaming ugc-image-upload user-follow-modify user-follow-read user-library-read user-library-modify user-read-private user-read-birthdate user-read-email user-top-read user-read-playback-state user-modify-playback-state user-read-currently-playing user-read-recently-played".split_whitespace().map(|x|x.to_owned()).collect::<Vec<String>>());
  let tok = TokenBuilder::default()
  .access_token("test-access_token")
  .expires_in(Duration::from_secs(3600))
  - .expires_at(Utc::now())
  + .expires_at(now)
  .scope(scope.clone())
  .refresh_token("...")
  .build()
  @@ -481,6 +482,8 @@ mod tests {
  assert_eq!(tok_str, tok_str_file);
  let tok_from_file: Token = serde_json::from_str(&tok_str_file).unwrap();
  assert_eq!(tok_from_file.scope, scope);
  + assert_eq!(tok_from_file.expires_in, Duration::from_secs(3600));
  + assert_eq!(tok_from_file.expires_at.unwrap(), now);
  }
  #[test]
  