Fix to fail if required arguments don't exist.

[yossan]

The missingArgument method isn't called now.

// <file> should be required but it works now.
program
  .argument('<file>')
  .parse(['node', 'test'])

These commits call the missingArgument method.

error: missing required argument `file`

[shadowspawn]

I have not worked through the code yet. A couple of questions @yossan (but you don't have to answer, it won't block my review, just make it easier):

• does this work correctly with multiple arguments too? .argument('<file> <env>')
• does this improve same situation with subcommands?

[yossan]

@shadowspawn

does this work correctly with multiple arguments too? .argument(' ')

// error: missing required argument `env'
program
    .arguments('<file> <env>')
    .parse(['node', 'test', 'setup'])

program
    .arguments('<file> <env>)
    .parse(['node', 'test', 'setup', 'path'])

does this improve same situation with subcommands?

This doesn't work.

program
    .command('cmd <file>')
    .parse(['node', 'test', 'cmd'])

I apologize. This commit may have caused subcommands not to work well.
I will fix it as soon as possible.

[shadowspawn]

See also: #896

[yossan]

@shadowspawn
I issued #995.

I think a fundamental review is necessary.