Workaround for JS error: "TypeError: h$concur is undefined"

[demaledetti]

These changes are inspired by package.json and webpack.config.js from https://github.com/concurhaskell/concur-react-starter ( eefa5d5 ) and their goal is to avoid a run-time JS error (TypeError: h$concur is undefined) that prevents the SortableTree component from displaying at all.

I am a webpack newbie so I might be very wrong but in my understanding these changes seem to contradict the advice given here:

https://github.com/concurhaskell/concur-react-starter#important-note-you-dont-need-to-add-react-and-reactdom-in-packagejson-as-those-dependencies-will-be-pulled-from-concur-react

"IMPORTANT NOTE: You don't need to add React and ReactDOM in package.json, as those dependencies will be pulled from Concur-React."

With these changes, the JS error doesn't happen and the SortableTree is displayed and works as expected.