看的书是 web 开发敏捷之道 rails 应用…第四版，使用的是 rails3.0.5。然后问题就出现了（之前用的是 4.0） rake 命令一直不能使用，出现的错误是这个样子的

rake aborted!
ERROR: 'rake/rdoctask' is obsolete and no longer supported. Use 'rdoc/task' (available in RDoc 2.4.2+) instead.
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/tasks/documentation.rake:1:in `require'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/tasks/documentation.rake:1:in `<top (required)>'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/tasks.rb:15:in `load'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/tasks.rb:15:in `block in <top (required)>'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/tasks.rb:14:in `each'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/tasks.rb:14:in `<top (required)>'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/application.rb:213:in `require'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/application.rb:213:in `initialize_tasks'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/application.rb:139:in `load_tasks'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/gems/railties-3.0.5/lib/rails/application.rb:77:in `method_missing'
/Users/donghaoran/work/demo/Rakefile:6:in `<top (required)>'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/bin/ruby_executable_hooks:15:in `eval'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/bin/ruby_executable_hooks:15:in `<main>'
(See full trace by running task with --trace)
donghaorandeMacBook-Air:demo donghaoran$ rake routes

我也装逼的在 stackoverflow 上发现了一个解决之道，是修改 rakefile，哈哈 最后还是不能生效，运行结果是这样的：

LoadError: cannot load such file -- tasks/rails
/Users/donghaoran/work/depot/Rakefile:8:in `require'
/Users/donghaoran/work/depot/Rakefile:8:in `<top (required)>'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/bin/ruby_executable_hooks:15:in `eval'
/Users/donghaoran/.rvm/gems/ruby-2.0.0-p481/bin/ruby_executable_hooks:15:in `<main>'
(See full trace by running task with --trace)

搜索发现发现是 rails3.0.5 必须使用 rake0.8.7 才行，可是 rake 现在默认的是 0.9.6，这个问题该怎么解决？