Fix navigationBarColor in modals

closes #1694

android/app/src/main/java/com/reactnativenavigation/screens/Screen.java

 package com.reactnativenavigation.screens;
 
 import android.annotation.TargetApi;
-import android.app.Activity;
 import android.content.res.Configuration;
 import android.graphics.Color;
 import android.os.Build;
     public void setNavigationBarColor(StyleParams.Color navigationBarColor) {
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) return;
 
-        final Activity context = (Activity) getContext();
-        final Window window = context.getWindow();
+        final Window window = ((NavigationActivity) activity).getScreenWindow();
         if (navigationBarColor.hasColor()) {
             window.setNavigationBarColor(navigationBarColor.getColor());
         } else {