Could not find generator active_admin:install (Rails 4.2.6)

[cucho]

$ rails g active_admin:install
Could not find generator 'active_admin:install'. Maybe you meant 'active_record:model', 'active_record:migration' or 'test_unit:model'
Run `rails generate --help` for more options.

In the Gemfile

....
gem 'devise'
gem 'activeadmin', github: 'activeadmin'
...

In Gemfile.lock

...
GIT
  remote: git://github.com/activeadmin/activeadmin.git
  revision: 0a5a15b88bffbe5efad7ff2a072ec4fe6eb09511
  specs:
    activeadmin (1.0.0.pre4)
      arbre (~> 1.0, >= 1.0.2)
      bourbon
      coffee-rails
      formtastic (~> 3.1)
      formtastic_i18n
      inherited_resources (~> 1.6)
      jquery-rails
      jquery-ui-rails
      kaminari (~> 0.15)
      railties (>= 3.2, < 5.1)
      ransack (~> 1.3)
      sass-rails
      sprockets (< 4.1)
...

[cucho]

Problem was with spring. I stopped it and rerun the generator and worked.