title: Operation not permitted - /usr/bin/update_rubygems
body: <p>When I execute on osx El Capitan:</p>
  
  <pre><code>sudo gem update --system  
  </code></pre>
  
  <p>I got the error:</p>
  
  <pre><code>Updating rubygems-update
  ERROR:  While executing gem ... (Errno::EPERM)
      Operation not permitted - /usr/bin/update_rubygems
  </code></pre>