Berks package not producing tarballs compatible with chef-solo

This seems to be a regression of #749 in that the tarball does not contain a cookbooks directory

The current code looks like this:

```ruby
    def package(path)
      packager = Packager.new(path)
      packager.validate!

      outdir = Dir.mktmpdir do |temp_dir|
        source = Berkshelf.ui.mute do
          vendor(File.join(temp_dir, 'cookbooks'))
        end
        packager.run(source)
      end

      Berkshelf.formatter.package(outdir)
      outdir
    end
```

looks like it would work as required if changed to

```ruby
        packager.run(outdir)
```

It's a simple change and i could look into submitting a pull request only I'll have a learning curve to go through in order to verify it.