This was a bug in a supporting library (Ridley) that Berkshelf 1.4.4 was tied to. It has since been resolved in Berkshelf 1.4.5.
You should uninstall and re-install vagrant-berkshelf to receive the updates. This can be accomplished by running:
$ vagrant plugin uninstall vagrant-berkshelf $ vagrant plugin install vagrant-berkshelf
Of course, this will also be resolved once vagrant-berkshelf is updated for Berkshelf 2.0.
If you run into a bug like this feel free to post it on the issue tracker on the Berkshelf or Vagrant-Berkshelf projects. It'll get the attention it deserves and a quick answer ;)