Rejected promises log `true`

```
vorpal
.command('fail me ')
.description('Must return an arg.')
.action(function (args) {
return new Promise(function (resolve, reject) {
if (args.arg === 'not') {
resolve('we are happy');
} else {
reject('we are not happy.');
}
});
});
```

```
$ fail me

Missing required argument. Showing Help:

Usage: fail me [options]

Must return an arg.

Options:

--help output usage information

$ fail me foo
true
```