message: [cmd] get_block_by_number support  short option.
diff: @@ -11,7 +11,7 @@ use structopt::StructOpt;
  #[derive(Debug, StructOpt)]
  #[structopt(name = "get_block_by_number")]
  pub struct GetOpt {
  - #[structopt(name = "number", long, default_value = "0")]
  + #[structopt(name = "number", long, short = "n", default_value = "0")]
  number: usize,
  }
  