title: Difference between `update_rubygems` and `gem update --system`
body: <p>What is the difference between this command:</p>
  
  <pre><code>gem update --system
  </code></pre>
  
  <p>And these commands:</p>
  
  <pre><code>gem install rubygems-update
  update_rubygems
  gem update --system
  </code></pre>
  
  <p>I would've assumed that the former would be all that is required in order to update to the latest version of RubyGems, but I have found many references (including <a href="https://stackoverflow.com/a/13626200/1369417">https://stackoverflow.com/a/13626200/1369417</a>) which recommend the latter.</p>