message: Simplify check_alias() using flatten()
diff: @@ -85,10 +85,7 @@ fn try_help(config: &Config) -> CargoResult<bool> {
  ///
  /// Returns None if it is not an alias.
  fn check_alias(config: &Config, subcommand: &str) -> Option<Vec<String>> {
  - match aliased_command(config, subcommand) {
  - Ok(Some(alias)) => Some(alias),
  - _ => None,
  - }
  + aliased_command(config, subcommand).ok().flatten()
  }
  /// Checks if the given subcommand is a built-in command (not via an alias).
  