"YAML Frontmatter: Error" in server logs

I'm a bit of a neophyte in the Ruby field, so it may be only ignorance, but to make YAML Frontmatter work properly on my machine I had to add the following line at the beginning of [response.rb](https://github.com/knuton/stubb/blob/master/lib/stubb/response.rb)
```ruby
require 'yaml'
```

I'm on a debian wheezy with ruby 1.9.3.