title: I updated my ipython notebook gist, but why didn't nbviewer update?
body: <p>I updated an ipython notebook gist here:</p>
  
  <p><a href="https://gist.github.com/rsignell-usgs/aa12c2b5e8a448bda780">https://gist.github.com/rsignell-usgs/aa12c2b5e8a448bda780</a></p>
  
  <p>but the nbviewer link here: </p>
  
  <p><a href="http://nbviewer.ipython.org/gist/rsignell-usgs/aa12c2b5e8a448bda780">http://nbviewer.ipython.org/gist/rsignell-usgs/aa12c2b5e8a448bda780</a></p>
  
  <p>is still displaying my old notebook.   I tried refreshing clearing the browser cache, but it still displays the old notebook.  </p>
  
  <p>Shouldn't it update?</p>