title: instant run not working: forcing kill and restart app
body: <p>instant run worked for me and I don't know why it stopped:
  I see the thunderbolt icon of the instance run but when I click it,  a popup appears :</p>
  
  <p>"Restart App?
  The app is already running. Would you like to kill it and restart the session?"
  the available options are "restart app"\ "cancel"</p>
  
  <p>when restart popup is shown :
  "Instant Run is disabled: variant 'debug' uses an unsupported feature (e.g. ProGuard)"</p>
  
  <p>(I've tried to comment progourd in gradle- didn't help)</p>
  
  <p>what am I missing?</p>