Rails的未定义方法“env”:模块

我想和RoR一起测试一下MongoDB的水域。我正在尝试使用以下命令创建项目:

rails mono_test_app -m http://gist.github.com/raw/284753/b5584c78fb5d29ab39a8218090801ea89b95a541/Rails%20MongoMapper%20Template

部分输出为

create  log/test.log
    applying  template: http://gist.github.com/raw/284753/b5584c78fb5d29ab39a8218090801ea89b95a541/Rails%20MongoMapper%20Template
   executing  rm public/index.html from /Users/olle/Projects/mono_test_app
   executing  rm public/images/rails.png from /Users/olle/Projects/mono_test_app
   executing  rm public/javascripts/controls.js from /Users/olle/Projects/mono_test_app
   executing  rm public/javascripts/dragdrop.js from /Users/olle/Projects/mono_test_app
   executing  rm public/javascripts/effects.js from /Users/olle/Projects/mono_test_app
   executing  rm public/javascripts/prototype.js from /Users/olle/Projects/mono_test_app
        file  app/views/layouts/application.html.erb
              What should I call the database? 
experiment
undefined method `env' for Rails:Module
Projects olle$ 

我用-m参数指定的模板包含

# MongoDB FTW!
db_name = ask('What should I call the database? ')

initializer 'database.rb', <<-CODE
MongoMapper.database = "#{db_name}-#{Rails.env}"
CODE

file 'config/database.yml', <<-CODE
# Using MongoDB
CODE

Github上的所有人似乎都分叉或克隆了Gist,并似乎在使用它,为什么在我的系统上会发生此错误?我错过什么了吗?

我在OSX和Ubuntu上都试过 Ruby1.8.7(2008-08-11补丁级别72)[I686-Darwin9.7.0] Rails 2.3.3