title: shrinkResources true can't be used on Instant Apps Feature?
body: <p>When I try to shrink my Feature APK size, I use <code>shrinkResources true</code> in my feature Build Gradle.
  However it complaints <code>Error:Resource shrinker cannot be used for libraries.</code></p>
  
  <p>This article ask us to use it
  <a href="https://medium.com/jet-stories/make-your-app-instant-33855ab5d02b" rel="noreferrer">https://medium.com/jet-stories/make-your-app-instant-33855ab5d02b</a></p>
  
  <p>Did I do something wrong or is this really not supported by Instant Apps?</p>