ruby-on-rails-4 – Rails 4：activeadmin错误消息 – Bundler找

gem 'activeadmin'

并更新了捆绑包,但收到此错误消息 –

Resolving dependencies...
Bundler could not find compatible versions for gem "actionpack":
  In Gemfile:
    activeadmin (>= 0) ruby depends on
      actionpack (~> 3.0.0.rc2) ruby

    rails (= 4.0.0) ruby depends on
      actionpack (4.0.0)

我在github上传了这个项目;这是gemfile的链接 – https://github.com/Mashpy/esl/blob/master/Gemfile

source 'https://rubygems.org'

# Bundle edge Rails instead: gem 'rails',github: 'rails/rails'
gem 'rails','4.0.0'

# Use sqlite3 as the database for Active Record
gem 'sqlite3'

# Use SCSS for stylesheets
gem 'sass-rails','~> 4.0.0'

# Use Uglifier as compressor for JavaScript assets
gem 'uglifier','>= 1.3.0'

# Use CoffeeScript for .js.coffee assets and views
gem 'coffee-rails','~> 4.0.0'

# See https://github.com/sstephenson/execjs#readme for more supported runtimes
# gem 'therubyracer',platforms: :ruby

# Use jquery as the JavaScript library
gem 'jquery-rails'

# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks'

# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder','~> 1.2'

#gem
 gem 'activeadmin'

group :doc do
  # bundle exec rake doc:rails generates the API under doc/api.
  gem 'sdoc',require: false
end

我做错了什么阻止我添加activeadmin？