Rubyonrails 如何解决 Heroku 上未初始化的常量 Rake：：DSL 问题

我得到的错误与in these questions的错误相似，但我的错误发生在Heroku:

2011-05-30T09:03:29+00:00 heroku[worker.1]: Starting process with command: `rake jobs:work`
2011-05-30T09:03:30+00:00 app[worker.1]: (in /app)
2011-05-30T09:03:30+00:00 heroku[worker.1]: State changed from starting to up
2011-05-30T09:03:33+00:00 app[worker.1]: rake aborted!
2011-05-30T09:03:33+00:00 app[worker.1]: uninitialized constant Rake::DSL
2011-05-30T09:03:33+00:00 app[worker.1]: /app/.bundle/gems/ruby/1.9.1/gems/rake-0.9.0/lib/rake/tasklib.rb:8:in `<class:TaskLib>'

这些问题的答案似乎是指定gem 'rake', '0.8.7'，因为0.9版本会导致问题.

当我试图将gem 'rake', '0.8.7'添加到我的gemfile并推送到Heroku时，我得到以下错误:

Unresolved dependencies detected; Installing...
You have modified your Gemfile in development but did not check
the resulting snapshot (Gemfile.lock) into version control

You have added to the Gemfile:
* rake (= 0.8.7)
FAILED: http://devcenter.heroku.com/articles/bundler
! Heroku push rejected, failed to install gems via Bundler
error: hooks/pre-receive exited with error code 1
To git@heroku.com:my_app.git
! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:my_app.git'

我的gemfile在Heroku上正常工作.我该怎么办？