title: Gradle exclude classes from aar
body: <p>Im using lib Gson in my dependecies and im import a .aar with some classes from Gson that are imported to a project.
  When i build my project i keep getting duplicated classes, bcz its on my dependency and aar classes.</p>
  <p>How i can exclude gson classes from aar?</p>
  <p>I have been trying with:</p>
  <ul>
  <li>exclude group: I think this is not work since is not a dependency from aar, but classes inside.</li>
  <li>transitive true, same reason as before</li>
  </ul>
  <p>Can i do it? or should i get other .aar with gson as dependecy?</p>