Create a script to update properties in package.json files

[gr2m]

My particular use case is to update the exports key in some of the @octoherd scripts.

For example:

https://github.com/octoherd/script-setup-renovate/blob/77901dcbb333ffa179585a99d23ffa9c01fbdb0e/package.json#L15

The exports path is ./index.js, but it should be ./script.js.