rspec – Capybara 2.1错误未初始化的常量Rails(NameError)

我刚将Capybara Gem从版本1升级到2.1.0(最新版本).基于Capybara Readme,我将以下行添加到Spork.prefork块中的spec_Helper.rb

require 'capybara/rspec'
require 'capybara/rails'

但是,我有一个错误

/home/user_1/.rvm/gems/ruby-1.9.3-p392/gems/capybara-2.1.0/lib/capybara/rails.rb:6:in `block (2 levels) in <top (required)>': uninitialized constant Rails (NameError)

我有没有想过有什么事情要求水瓶座正常工作？

require 'rspec/rails'

require 'capybara/rspec'
require 'capybara/rails'