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[Rich-Harris]

Adds a pkg.exports field. Today, if you import sirv in a "type": "module" app, it will import build.js rather than build.mjs. With this change, build.mjs is imported. Not that it actually makes a difference.

[lukeed]

Adding exports is a breaking change on its own. Cutting a new major solely for this does more harm than good, especially since sirv actually works fine in Node ESM (given native ESM interop).

Will include this once there's actually a change in functionality to constitute a sirv@3.x release.