This method has the following issues:

• when registered subcommand, thier arguments and options isn't parsed to check valid.
• when registered action, this.parseArgs() called subcommand without parsing their arguments and options.

As a result, this method's arguments are not evaluted correctly in subcommand.
In the following code expect to occur error: missing required argument "file" but not now.

parse
  .command('install <file>')
  .parse('node', 'main.js', 'install') // Expect error but not.

Also now the required argument will not correctly work.
Fix to fail if required arguments don't exist.

So it seems that this method should be reconsidered fundamentally.

Thank you for the wonderful library.

Related

#941