whatwg-fetch removed from production bundle

[gaelollivier]

I am trying to use whatwg-fetch to polyfill fetch on IE 11. Snowpack seems to override node-fetch and whatwg-fetch with a native polyfill. In the code, it says this should still allow to polyfill in older browsers: https://github.com/snowpackjs/snowpack/blob/fc6c1417a09ac85e02730033660391d299a5fd97/esinstall/src/rollup-plugins/rollup-plugin-catch-fetch.ts#L28

However I don't see how I am supposed to achieve this. I made a small reproduction repository where I pushed the output from yarn build: https://github.com/gaelduplessix/snowpack-app/blob/whatwg-fetch/build/_snowpack/pkg/whatwg-fetch.js

whatwg-fetch is replaced by snowpack and prevents it from being included in my production bundle. I am not sure if this is a bug in snowpack or if there is another recommended way to include polyfills? Thanks!