undefined_method `author=` for Quarto::Module when running rake deliverables

I tried to run `rake deliverables` with the following Rakefile:

``` ruby
require 'quarto'

Quarto.configure do |config|
  config.author          = "Avdi Grimm"
  config.title               = "Confident Ruby"
end
```

Just as it is prescribed in the README, but got the error message in the subject line.

What am I doing wrong?
