title: git submodule update fatal error: reference is not a tree
body: <pre><code>user$ sudo git submodule update
  fatal: reference is not a tree: a094dcfeeb43fcd62a9e466156e05e7581026f33
  Unable to checkout 'a094dcfeeb43fcd62a9e466156e05e7581026f33' in submodule path 'client/src/util'
  </code></pre>
  
  <p><strong>What do I do? I just want to get a clean copy of the latest code from the repo, i dont mind losing my changes.</strong>  As you can tell, I clearly am not sure what is happening. I can only think that it is trying to checkout a file which means git detected a local change in a file on my local machine.</p>
  
  <p>i am currently using OSX</p>