Fix possible crash (#771)

Crash description here
http://stackoverflow.com/questions/7575921/illegalstateexception-can-not-perform-this-action-after-onsaveinstancestate-wit

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

         FragmentManager fm = activity.getFragmentManager();
         FragmentTransaction transaction = fm.beginTransaction();
         transaction.add(R.id.fragment_screen_content, fragment);
-        transaction.commit();
+        transaction.commitAllowingStateLoss();
     }
 
     private void addSupportFragment(android.support.v4.app.Fragment supportFragment) {
         android.support.v4.app.FragmentManager fm = activity.getSupportFragmentManager();
         android.support.v4.app.FragmentTransaction transaction = fm.beginTransaction();
         transaction.add(R.id.fragment_screen_content, supportFragment);
-        transaction.commit();
+        transaction.commitAllowingStateLoss();
     }
 
     @Nullable