This workflow failed for me and this forum entry appears to break down the reason why:
http://www.alfredforum.com/topic/3173-ruby-workflows-in-mavericks/page-2
Since my ruby skills are lacking (and I've been trying to pick up more python) I switched to this workflow and it is working flawlessly under Mavericks:
http://db.tt/HyUXaHsF source thread
The only drawback is that I had to switch to a new keyboard shortcut since Alfred wouldn't allow me to enter option+shift+d for this workflow.