Can't create UMD build which can be required by Node #6522

Do you want to request a feature or report a bug?

bug

What is the current behavior?

If you require a module in the target output UMD you get this error:

ReferenceError: window is not defined
    at Object.<anonymous> (/mnt/c/Users/foo/webpack-umd-node/dist/main.js:1:272)

If the current behavior is a bug, please provide the steps to reproduce.

• https://github.com/donaldpipowitch/webpack-umd-node
• $ git clone git@github.com:donaldpipowitch/webpack-umd-node.git && cd webpack-umd-node && yarn && yarn build && yarn test

What is the expected behavior?

You shouldn't see a ReferenceError.

If this is a feature request, what is motivation or use case for changing the behavior?

Please mention other relevant information such as the browser version, Node.js version, webpack version, and Operating System.

Node v8.9.4, webpack v4.0.0-beta.2

According to https://webpack.js.org/configuration/output/#module-definition-systems the UMD build should not include window.