尝试执行时：
rake db:migrate
终端回答：
rake aborted!
ERROR: 'rake/rdoctask' is obsolete and no longer supported. Use 'rdoc/task' (available in RDoc 2.4.2+) instead.
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/tasks/documentation.rake:1:in `require'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/tasks/documentation.rake:1:in `<top (required)>'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/tasks.rb:15:in `load'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/tasks.rb:15:in `block in <top (required)>'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/tasks.rb:6:in `each'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/tasks.rb:6:in `<top (required)>'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/application.rb:213:in `require'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/application.rb:213:in `initialize_tasks'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/application.rb:139:in `load_tasks'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/gems/railties-3.0.5/lib/rails/application.rb:77:in `method_missing'
/Users/Charles/rails_projects/demo_app/Rakefile:7:in `<top (required)>'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/bin/ruby_noexec_wrapper:14:in `eval'
/Users/Charles/.rvm/gems/ruby-1.9.3-p429@rails3tutorial/bin/ruby_noexec_wrapper:14:in `<main>'
(See full trace by running task with --trace)
此处提出的任何解决方案（特别是降级 gem，或修改 Rakefile（以下）工作（rake 版本 10.0.1）
require File.expand_path('../config/application', __FILE__)
require 'rake'
DemoApp::Application.load_tasks
谢谢您的帮助，