Fix broken documentation.

The missing comment on line 17 breaks rdoc and yard, resulting in the documentation ([rdoc](http://www.ruby-doc.org/gems/docs/s/sprinkle-0.7.6.2/Sprinkle/Installers/Installer.html), [yard](http://rubydoc.info/gems/sprinkle/Sprinkle/Installers/Installer)) starting with a "note about sudo".