message: [cmd] rename LogLevelOpt's level to default argument.
diff: @@ -11,7 +11,7 @@ use structopt::StructOpt;
  #[derive(Debug, StructOpt)]
  #[structopt(name = "loglevel")]
  pub struct LogLevelOpt {
  - #[structopt(short = "l")]
  + #[structopt(name = "level")]
  level: Level,
  }
  