title: How can I force gem to upgrade to gem 1.3.1
body: <p>I am trying to install a gem like this:</p>
  
  <pre><code>C:\InstantRails\rails_apps\foodmarksthespot&gt;ruby script/plugin install git://github.com/lazyatom/engines.git
  </code></pre>
  
  <p>Which returns this message:</p>
  
  <pre><code>Rails requires RubyGems &gt;= 1.3.1 (you have 1.2.0). Please `gem update --system` and try again.
  </code></pre>
  
  <p>But when I try to update using:</p>
  
  <pre><code>gem update --system
  </code></pre>
  
  <p>it says:</p>
  
  <pre><code>Updating RubyGems
  Nothing to update
  </code></pre>
  
  <p>This is on windows. How can I force it to upgrade the system to a specific version?</p>