title: error when run rvm requirements
body: <p>I followed
  <a href="http://blog.sudobits.com/2012/05/02/how-to-install-ruby-on-rails-in-ubuntu-12-04-lts/">this tutorial</a>
  to install rvm on ubuntu 12.04
  when run <code>rvm requirements</code>, I got the following message</p>
  
  <pre><code>Installing requirements for ubuntu, might require sudo password.
  Running 'apt-get --quiet --yes update' would require sudo.
  Cowardly refusing to continue, please read 'rvm autolibs'.
  Updating repositories
  Missing required packages: libgdbm-dev, libffi-dev.
  Cowardly refusing to continue, please read 'rvm autolibs'.
  </code></pre>
  
  <p>I got same message when run <code>rvm install 1.9.3</code></p>
  
  <p>Can anyone help?</p>
  
  <p>Thanks.</p>