Fixes berks upload

Berks upload fails, because the files directory directly contains a file.

```
>berks upload yum-mysql-community
E, [2014-06-11T17:48:56.687187 #732] ERROR -- : Ridley::Errors::HTTPBadRequest: {"error":["Invalid element in array value of 'files'."]}
E, [2014-06-11T17:48:56.689187 #732] ERROR -- : C:/opscode/chef/embedded/lib/ruby/gems/1.9.1/gems/ridley-4.0.0/lib/ridle
y/middleware/chef_response.rb:24:in `on_complete'
C:/opscode/chef/embedded/lib/ruby/gems/1.9.1/gems/faraday-0.9.0/lib/faraday/response.rb:9:in `block in call'
C:/opscode/chef/embedded/lib/ruby/gems/1.9.1/gems/faraday-0.9.0/lib/faraday/response.rb:57:in `on_complete'
C:/opscode/chef/embedded/lib/ruby/gems/1.9.1/gems/faraday-0.9.0/lib/faraday/response.rb:8:in `call'
C:/opscode/chef/embedded/lib/ruby/gems/1.9.1/gems/faraday-0.9.0/lib/faraday/response.rb:8:in `call'
```