当我$bundle install --without production，我得到这个：
An error occured while installing nokogiri (1.5.5), and Bundler cannot continue.
Make sure that `gem install nokogiri -v '1.5.5'` succeeds before bundling.
我的 gemfile 看起来像这样：
source 'https://rubygems.org'
gem 'rails', '3.2.8'
group :development, :test do
gem 'sqlite3', '1.3.5'
gem 'rspec-rails', '2.11.0'
end
# Gems used only for assets and not required
# in production environments by default.
group :assets do
gem 'sass-rails', '3.2.5'
gem 'coffee-rails', '3.2.2'
gem 'uglifier', '1.2.3'
end
gem 'jquery-rails', '2.0.2'
group :test do
gem 'capybara', '1.1.2'
end
group :production do
gem 'pg', '0.12.2'
end