The isPrivateS3Scheme method does not handle default private

\Drupal\flysystem_s3\File\FlysystemS3FileSystem::isPrivateS3Scheme does not handle the default value for the ACL being private. If the configuration option is not present, the code handles that as 'private', but in this case the method returns a FALSE.

Will add a patch to fix the issue.

ps. under version, I could not select 2.0.x. But since both branches are (almost) identical in code, the patch should apply to all :)