title: gesturesEnabled: false doesn't work for my react-navigation setup
body: <pre><code>    export const AppNavigator = StackNavigator({
          [strings.route_login]: {
              screen: LoginScreen,
          },
          [strings.route_main]: {
              screen: MainNavigator,
              navigationOptions: {
                  gesturesEnabled: false,
              }
          },
      },
      {
          headerMode: "none",
          navigationOptions: {
              gesturesEnabled: false,
          }
      }
  );
  </code></pre>
  
  <p>I'd like to mention also that the MainNavigator is a DrawerNavigator and all it's children have the gesturesEnabled turned off! Unfortunately I can still swipe back to the LoginScreen in ios!</p>