Can't use webpack 4 with alpha branch

[seanmacisaac]

Describe the bug
Due to the typescript target and module setting of esnext the alpha branch can't be used with webpack 4. Changing this to es6 (or es2015) resolves the issue.

Additional context
We will eventually upgrade to webpack5, but for now have some things that would make that very difficult that we are waiting on maintainers of other projects to resolve. I've forked and have installed from our fork, but would prefer to reference the package on npmjs.com