Reference where types are
Reference where types are

Because of the `main` directive, typescript 2.9 now looks in `./lib/index.d.ts`
first, where it finds [this file](https://github.com/mlaursen/react-md/blob/master/src/js/index.d.ts).

This change specifically tells typescript to look at the `index.d.ts` in
the root of the built project.
mlaursen/react-md,mlaursen/react-md,mlaursen/react-md