make unpublished packages return 404 (#58)
make unpublished packages return 404 (#58)

unpublished packages return objects like this:

```js
{ _id: 'salesforce-alm',
  _rev: '3-33501e8dcd1f5aff5cc4e2e5156b8de0',
  name: 'salesforce-alm',
  time:
   { modified: '2016-12-07T16:28:02.949Z',
     created: '2016-12-07T13:50:24.788Z',
     '0.6.22': '2016-12-07T13:50:24.788Z',
     '0.6.23': '2016-12-07T13:52:31.994Z',
     unpublished:
      { name: 'cisfuser1',
        time: '2016-12-07T16:28:02.949Z',
        tags: [Object],
        maintainers: [Object],
        versions: [Object] } },
  _attachments: {} }
```
dickeyxxx/elephant,jdxcode/npm-register,dickeyxxx/elephant,dickeyxxx/npm-register,jdxcode/npm-register,heroku/elephant,heroku/elephant,dickeyxxx/npm-register