Fix worker example

[7rulnik]

What kind of change does this PR introduce?

bugfix for example. Currently, publicPath from config is ignored which leads to error when loading chunks inside the worker.

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[webpack-bot]

Thank you for your pull request! The most important CI builds succeeded, we’ll review the pull request soon.

[sokra]

Thanks