Refactor to support release-it@15 (ESM)

[refi93]

Motivation: refactor the package to work with release-it v15 which transitioned to ESM modules

Testing: run unit tests with yarn test

closes #68

[alvarlagerlof]

I tried copying the files in this pull request into my monorepo and I can confirm that it works for me. Successfully published.

[alvarlagerlof]

It looks like nothing has been committed to this repo since Oct 2021, the latest release in Apr that year. The author is not active. I think we should consider a fork. Are you interested in collaborating on one? @refi93

[refi93]

It looks like nothing has been committed to this repo since Oct 2021, the latest release in Apr that year. The author is not active. I think we should consider a fork. Are you interested in collaborating on one? @refi93

I see, I'm not sure if I would have the time for maintaining the fork long-term either, but of course, whoever can, feel free to pick these changes up and make it 👍

[scalvert]

@rwjblue has been out on holiday. I'm happy to take a look at this too. We don't need a fork.

I just finished a large ESM refactor myself, so hopefully can provide assistance.

[scalvert]

Since we're going to be releasing this as a breaking change, and the ESM conversion essentially opts us into ESM-land, it strikes me that we should remove release-it < 15 from the test matrix, since there's no expectation that we can use this plugin within release-it's versions that are CJS-based.

[scalvert]

It looks like we'll need to remove the required checks, but I don't have access to this repo's settings since it's under @rwjblue's personal GH user. I'll try to ping him to address this once he's back.