title: Why does running rake gems:unpack result in a Gem::FilePermissionError
body: <p>I'm attempting to upgrade the friendly_id gem in a rails project.</p>
  
  <p>I have removed the old gem from the vendor directory, installed the new gem from rubygems.org. When I type:</p>
  
  <pre><code>rake gems:unpack
  </code></pre>
  
  <p>I get the following response:</p>
  
  <pre><code>ERROR:  While executing gem ... (Gem::FilePermissionError)
      You don't have write permissions into the /usr/lib/ruby/gems/1.8 directory.
  </code></pre>
  
  <p>Sure, I realise I can sudo it, but what I don't understand is if I would like to unpack the gem into my project vender directory, why does it need access to /usr/lib/ruby/gems....</p>