title: ScrollView with flex 1 makes it un-scrollable
body: <p>I'm trying to run flex on a <code>ScrollView</code>, and as long as the ScrollView has <code>flex: 1</code> the <strong>scroll inside does not work</strong>. 
  here is the expo fiddle (that you can run this code and play with)
  <a href="https://snack.expo.io/SySerKNp-" rel="noreferrer">https://snack.expo.io/SySerKNp-</a></p>
  
  <p>note that if you remove the <code>flex: 1</code> from the <code>ScrollView</code> it does let scroll but then you lose the flex power ( the ability to let the red container down to push up the upper box (the ScrollView) ) so I must have a flex there.</p>
  
  <p>p.s - I'm working only on android, and I haven't tested it on iPhone( I don't mind the result there )</p>
  
  <p>any idea what am I missing ? why the <code>ScrollView</code> won't function right when it has a <code>flex: 1</code> ?
  thanks !</p>