title: Forcing package update with Mix
body: <p>When I use the following command</p>
  
  <p><code>mix deps.update --all</code></p>
  
  <p><code>mix</code> will use locally cached packages if the version of a package has not been changed in the <code>mix.ex</code> file. So the question is, how can I force <code>mix</code> not to use the cached version and download it from the server instead? For example,  if there were changes in the last version of some package and I want to pick those up, even if the version has not been bumped.</p>