Add `"sideEffects": false` to `package.json`

[neoncube2]

Can "sideEffects": false please be added to package.json? This can enable more tree-shaking, in some cases: documentation

In my case, specifically, I'm using react-string-replace conditionally during compilation, but Webpack is still including the library's code in the final bundle, because it's afraid it might have side effects.

Thanks! :)