[multibot] Add `sideEffects: false` to `package.json`

[ryan-roemer]

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:

• https://github.com/webpack/webpack/issues/1750

This PR should resolve the issues discussed in:

• https://github.com/FormidableLabs/victory/issues/549
• https://github.com/FormidableLabs/redux-little-router/issues/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. The transform code and documentation is available at: https://github.com/FormidableLabs/multibot-examples/tree/master/transforms/webpack-side-effects