shallowReadStream: Use only entry prefix for directory keys

[josephmturner]

This change makes drive.list(folder, { recursive: false }) return only the entry prefix key for directories.

Given that the root directory contains

/foo
/bar/baz
/bar/quux

Previously, drive.list('/', { recursive: false }) returned

{
  seq: 42,
  key: '/foo',
  value: { ... }
}
{
  seq: 43,
  key: '/bar/baz',  // Expected key: '/bar'
  value: { ... }
}

Now, drive.list('/', { recursive: false }) returns

{
  seq: 42,
  key: '/foo',
  value: { ... }
}
{
  key: '/bar',
}

Note that seq and value properties have been thrown away since they don't belong to the entry prefix.

[mafintosh]

Thats what readdir is for. List is for returning actual nodes

[josephmturner]

Thanks. That makes sense.