Just a heads up with the latest ruby and rails installed bundler threw errors but installed. So I investigated on removing or cleaning up the warning about registering. Was a rubygems issue, needed to run gem update --system 3.0.8 && gem update --system, once I did that it cleared up the error but created another issue.

When you got to the generate model if answered yes it would hang. Due to an issue with spring preloader, had to put in under your run 'bundle install',  run 'spring stop'

So the file now looks like:

 gem 'devise'

  run 'bundle install'
  run 'spring stop'
 
  if yes?("Do you want to generate a User Model (first_name, last_name, admin:boolean)?")
    generate(:model, 'user', 'first_name', 'last_name', 'admin:boolean')
 end

 # rails g devise:install
 generate('devise:install')
 generate(:devise, 'User')
 
 environment 'config.action_mailer.default_url_options = { host: "localhost", port: 3000 }', env: 'development'