Now that we no longer support IE we can raise the minimum ES target a
bit. Changing to es2015 shaves off ~17% from the main bundle size, also
it prevents generators from being transpiled into regular functions etc.
so I would guess it has the potential to give some general performance
improvements too.
For fun I also tried to raise it to es2022, this gave a slightly bigger
bundle than es2015 so I think es2015 could be an ok target unless we
need something newer for some reason.
Svante Boberg