Using Rails Composer, getting error "-bash: rails: command not found" using "learn-rails" gemset

Question

I'm using Nitrous on Windows 7, and trying to use RailsComposer following "Build ‘Learn Rails’ in Less Than Five Minutes" of the Learn Ruby on Rails book.

The book tells:

Use the “learn-rails” gemset we created earlier:

$ rvm use ruby-2.1.3@learn-rails

and then,

$ rails new foobar-kadigan -m https://raw.github.com/RailsApps/rails-composer/master/composer.rb

I have this error:

-bash: rails: command not found