Add a package-lock.json or yarn.lock

Hello :)

It's me again.

What happened:

When I tried to make a reproduction test in this repository, I encounter some difficulties with the dependencies because there is not lock files. Moreover, because there are some libraries overrides this is buggy.

Reproduction:

Follow CONTRIBUTING.md, i.e. :

• Clone the repo
• npm run setup -s

See the error with browserslist.

Problem description:

Because there is no lock files, the latest libraries are fetched. Unfortunately babel made some change on their @babel/helper-compilation-targets that pull the latest browserslist package which expose a new findConfigFile (which is not exposed in the override version)

In the issue https://github.com/testing-library/dom-testing-library/issues/1352 I had to do this to make the test reproduction works:

https://github.com/romain-trotard/dom-testing-library/blob/labelledby-multiple-repro/package.json#L83

Suggested solution:

I know that Kent is not fond of pushing lock files https://github.com/kentcdodds/kcd-scripts/issues/22#issuecomment-355061803.

But I wonder why it would be a problem to do it.

I think pushing it, would help a lot on the reproducibility.

Thanks in advance :)

Start with CONTRIBUTING.md and run npm run setup -s to reproduce the browserslist dependency error. Inspect package.json, including its overrides, and determine whether a package-lock.json or yarn.lock fits the repository's workflow. Done means the dependency versions are locked and setup completes reproducibly without the reported error.