title: "gem update --system is disabled on Debian" error
body: <p>When I try to update rubygems (by running 'gem update --system') I get this error:</p>
  
  <pre><code>ERROR:  While executing gem ... (RuntimeError)
  gem update --system is disabled on Debian. RubyGems can be updated using the official Debian repositories by aptitude or apt-get.
  </code></pre>
  
  <p>Any idea what might be wrong and how I can fix it?</p>