Bump berkshelf
Bump berkshelf

I hit an error running test kitchen:

```
rake aborted!
Failed to complete #converge action: [redirection forbidden: http://cookbooks.opscode.com/api/v1/cookbooks/minitest-handler/versions/1.3.2/download -> https://s3.amazonaws.com/community-files.opscode.com/cookbook_versions/tarballs/7243/original/minitest-handler20140730-17106-jeqp0g.tar.gz?1406769702]
```

Then found:

> This is fixed in Berkshelf 2.0.18
> --seen on https://github.com/berkshelf/berkshelf/issues/1252#issuecomment-48336031

I ran `bundle update berkshelf` and going from 2.0.13 to 2.0.18 seems to have resolved the issue.

onetwotrip/chef-golang,scalp42/chef-golang,NOX73/chef-golang,NOX73/chef-golang,NOX73/chef-golang,archsaber/chef-golang,rollbrettler/chef-golang,archsaber/chef-golang,scalp42/chef-golang,rollbrettler/chef-golang,mingderwang/chef-golang,rollbrettler/chef-golang,onetwotrip/chef-golang,GannettDigital/chef-golang,mingderwang/chef-golang,archsaber/chef-golang,GannettDigital/chef-golang,onetwotrip/chef-golang,GannettDigital/chef-golang,scalp42/chef-golang,mingderwang/chef-golang