fix default extension to cjs for package.json "type":"module"

[aheissenberger]

The old implementation will not allow to use a filename with the extension ".cjs" in the "main" field and does not create a Common JS file with a ".cjs" ending.

If a package.json contains "type":"module" all files with ".js" will throw an error if they are imported with an require function.

This fix:

• will strip .cjs when creating the base name
• switch from default extension .js to .cjs when "type":"module" exists in package.json
• update documentation to highlight the problem

This solves #801

[changeset-bot]

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Latest commit: 8d18bf2

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[developit]

Hiya - sorry for the delay on this PR, I'm actually thinking we might be better off detecting this and warning, rather than relying on docs ... I'm silly, and you already did this. Cheers!

[JounQin]

@developit There is no changeset generated for this PR.

[jeffryang24]

Hmm.. Can't wait this change to be published... 🙇

[developit]

This is published.