ruby-on-rails – 未定义的方法`use_transactional_fixtures

/home/***/***/***/spec/spec_helper.rb:27:in `block in <top (required)>': undefined method `use_transactional_fixtures=' for #<RSpec::Core::Configuration:0x9fe8824> (NoMethodError)

我的宝石如下：

gem "rspec-rails",:group => [:test,:development]
group :test do
    gem "factory_girl_rails"
    gem "capybara"
    gem "guard-rspec"
end

我的配置文件如下：

# This file is copied to spec/ when you run 'rails generate rspec:install'
ENV["RAILS_ENV"] ||= 'test'
require File.expand_path("../../config/environment",__FILE__)
require 'rspec/rails'
require 'rspec/autorun'
require 'capybara/rspec'

# Requires supporting ruby files with custom matchers and macros,etc,# in spec/support/ and its subdirectories.
Dir[Rails.root.join("spec/support/**/*.rb")].each {|f| require f}

RSpec.configure do |config|
  # ## Mock Framework
  #
  # If you prefer to use mocha,flexmock or RR,uncomment the appropriate line:
  #
  # config.mock_with :mocha
  # config.mock_with :flexmock
  # config.mock_with :rr

  # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
  # config.fixture_path = "#{::Rails.root}/spec/fixtures"

  # If you're not using ActiveRecord,or you'd prefer not to run each of your
  # examples within a transaction,remove the following line or assign false
  # instead of true.
  config.use_transactional_fixtures = true

  # If true,the base class of anonymous controllers will be inferred
  # automatically. This will be the default behavior in future versions of
  # rspec-rails.
  config.infer_base_class_for_anonymous_controllers = false

  # Run specs in random order to surface order dependencies. If you find an
  # order dependency and want to debug it,you can fix the order by providing
  # the seed,which is printed after each run.
  #     --seed 1234
  config.order = "random"
end

那么为什么我在守卫跑的时候会出现这个错误？