Update package.json

[benmccann]

cleaning up a couple of issues from https://publint.dev/magic-string@0.30.10

module and jsnext:main will be ignored since exports is present

[antfu]

I am not sure how big the userbase magic-string has, especially since it's out for a very long while.

module and jsnext:main will be ignored since exports is present

In that case, I feel it won't hurt to keep those fields:

• Tools that support exports already ignore them
• Tools that don't support exports could still pick them up