title: How can I add gems to my vendor/cache directory in a Rails 3 app?
body: <p>I use EngineYard, and I have a deployment that is failing. I am getting this message:</p>
  
  <pre><code>Some gems seem to be missing from your vendor/cache directory.
  Could not find rspec-core-2.6.0.rc2 in any of the sources
  </code></pre>
  
  <p>How do I make sure those gems get in that directory?</p>