Hm, I'm trying it on Yosemite Dp6 and see this getting logged:
[ERROR: alfred.workflow.action.script] Code 127: /bin/bash: line 4: /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby: No such file or directory
[EDIT]
Never mind, I found that installing the "Experimental" mavericks version works.