message: [now-cli] Proper error message when `now alias` misses arguments
  We need to show a proper error message when `now alias` misses arguments.
diff: @@ -65,6 +65,13 @@ export default async function set(
  return 1;
  }
  + if (args.length < 2) {
  + output.error(
  + `${cmd('now alias <deployment> <target>')} requires two arguments`
  + );
  + return 1;
  + }
  +
  if (args.length >= 1 && !isValidName(args[0])) {
  output.error(
  `The provided argument "${args[0]}" is not a valid deployment`
  