Update to upstream release of rollup-plugin-node-resolve after mainfields feature lands

[gregmagolan]

In order to support the es2015 package.json attribute we had to use a custom dist of rollup-plugin-node-resolve based on 4.0.0 here: #429. The code for it is here: rollup/rollup-plugin-node-resolve#186

Once rollup/rollup-plugin-node-resolve#182 lands in rollup-plugin-node-resolve and it makes it into a release we can go back to an upstream version and use make use of the new mainfields feature from #182 to support es2015 in internal/rollup/rollup.config.js.