webpack@4 / webpack@next will support `package.json:sideEffects: …

…false` wherein libraries can indicate their ESM re-exports are side effect free and can be much more efficiently removed for smaller, faster final bundles.

Lodash has already rolled out this change in
https://unpkg.com/lodash-es@4.17.5/package.json

## Issues

This was originally uncovered / discussed at length in:

* webpack/webpack#1750

This PR should resolve the issues discussed in:

* FormidableLabs/victory#549
* FormidableLabs/redux-little-router#262

## Changes

* Add `sideEffects: false` to `package.json` to allow webpack4 tree-shaking to actually remove all unused code.

> This PR has been automatically opened by your friendly [`multibot`](https://github.com/FormidableLabs/multibot/). The transform code and documentation is available at: https://github.com/FormidableLabs/multibot-examples/tree/master/transforms/webpack-side-effects

package.json

@@ -135,5 +135,6 @@
     "files": {
       ".npmignore": ".npmignore.publishr"
     }
-  }
+  },
+  "sideEffects": false
 }