title: Make app free for users who already purchased previous versions
body: <p>Suppose I upload my app (version 1.0) to App store with a price of 1.99 USD. Later I'll upload a version(1.1) with some upgradations but again with a same price tag(1.99 USD). I want my previous users(who purchased version 1.0) to download the version 1.1 for free.</p>
  
  <p>How can I do that?</p>