title: Firebase user property boolean value. (true or false)
body: <p>I want to have some way to see how many percent of my app's users have purchased the "premium upgrade".</p>
  
  <p>The premium upgrade can be purchased one time, through an in app purchase. The <code>boolean</code> value is stored on the device by Google Play. I would like to see that 'value' in Firebase.</p>
  
  <p>I thought about setting a user property with the name <strong>Premium</strong>, but can't find out how I can set the value to <code>true</code> or <code>false</code>.</p>
  
  <p>Is this the correct way, or is there a better method for just a <code>boolean</code> value?</p>