title: Kivy: dismiss() doesn't work on my ModalView widget
body: <p>I am making a <code>ModalView</code> widget and trying to close it by pressing a button on it. The callback of the button press goes to method that suppose to close it.</p>
  
  <p>This is main.kv:</p>
  
  <pre><code>&lt;MainFrame&gt;:
      id: main_frame
      ScreenMaster:
          id: screen_master
          StartScreen:
              id: start_screen
              SettingsPopup:
                  id: settings_popup
          GameScreen:
              id: game_screen
              GameOverPopup:
                  id: gameover_popup
  </code></pre>
  
  <p>And gameoverpopup.kv:</p>
  
  <pre><code>&lt;GameOverPopup&gt;:
      auto_dismiss: False
      pos_hint: {'center_x': .5, 'center_y': .5}
      size_hint: .7, .4
      RelativeLayout:
          Button:
              id: close_button
              pos_hint: {'x': .1, 'y': .05}
              size_hint: .8, .2
              text: 'PLAY AGAIN'
              on_press: root.done()
          Label:
              pos_hint: {'x': .2, 'y': .8}
              size_hint: .6, .15
              font_size: 32
              text: 'YOU WON'
  </code></pre>
  
  <p>And main.py:</p>
  
  <pre><code># kivy includes
  Builder.load_file('startscreen.kv')
  Builder.load_file('gamescreen.kv')
  Builder.load_file('settingspopup.kv')
  Builder.load_file('gameoverpopup.kv')
  
  class StartScreen(Screen):
      pass
  
  class GameScreen(Screen):
      pass
  
  class ScreenMaster(ScreenManager):
      pass
  
  class SettingsPopup(ModalView):
      pass
  
  class GameOverPopup(ModalView):
      def done(self):
          self.dismiss()
  
  class MainFrame(AnchorLayout):
      pass
  
  class MainApp(App):
      def on_pause(self):
          return True
  
      def build(self):
          return MainFrame()
  
  if __name__ == '__main__':
      MainApp().run()
  </code></pre>
  
  <p>Pressing <code>Play again</code> button calls <code>done()</code> method, but the <code>ModalView</code> widget doesn't dismiss. How can I solve this problem and make it disappear?</p>