function createSubCommand(name, targetVersionRange, description) {
  const migration = {
    name: name,
    description: description,
    range: targetVersionRange,
  };
  migrations.push(migration);

  return new Command(name)
    .description(description)
    .requiredOption('--from <from-version>', 'Blockly version to migrate from')
    .option('--to <to-version>', 'Blockly version to migrate to')
    .argument('<file...>', 'Files to migrate');
}
Creates a command with the basic format expected by the migrate script,
and automatically adds it as a subcommand. It is then returned so it can be
configured.
@param {string} name The name of the subcommand.
@param {string} targetVersionRange The range of target versions of Blockly
    this command assists in migrating to.
@param {string} description The description of the new subcommand.
@returns {!Command} The basic subcommand.