Upgrade a rails 3

Sto cercando di fare l’upgrade di alcune applicazioni.
Come indicato in
Ruby on Rails 3.0 Release Notes — Ruby on Rails Guides ho installato
il plugin rails_upgrade ruby script/plugin install
GitHub - rails/rails_upgrade: Plugin to run checks on your Rails 2.x/3.x to check for obvious upgrade points on the path to 3.0.
Una volta installato il comando rake rails:upgrade:check mi dice
rake aborted!
no such file to load – initializer

cosa mi manca.