title: bundle install can not be executed and causes error on rails production server
body: <p>We use capistrano for rails deployment. Here is a strange error when running <code>bundle install</code> on production server.</p>
  
  <pre><code>You are trying to install in deployment mode after changing
  your Gemfile. Run `bundle install` elsewhere and add the
  updated Gemfile.lock to version control.
  
  If this is a development machine, remove the Gemfile freeze
  by running `bundle install --no-deployment`.
  
  You have added to the Gemfile:
  * rails (= 3.1.3)
  * mysql2 (&gt;= 0.2.6)
  
  You have deleted from the Gemfile:
  * rails (~&gt; 3.1.3)
  </code></pre>
  
  <p>Gemfile on production server was manually changed and then, this error comes out. This is a new production server and we plan to run rails 3.1.3. We rebooted the linux server and it did not help. Is there way to fix the problem? thanks so much.</p>