Update package.json devDependency versions

[dd32]

While investigating #541 and #542 I tried updating the modules, I guess we should probably do that at some point? I don't know what (if anything) this would break/fix.

[ryelle]

I guess we should probably do that at some point? I don't know what (if anything) this would break/fix.

A quick glance at the changelogs, not much for env, some new linter rules in eslint-plugin, scripts updated stylelint, and I don't know about puppeteer — I think we're just using that for the screenshot changes though.

The lint error here is due to the scripts' stylelint upgrade, I have a PR into the repo-tools repo to update the stylelint rules: WordPress/wporg-repo-tools#32

Is it possible to tell composer to install that branch of repo-tools? I don't think we can merge that until all the projects can be updated. Actually… if we switch to a js config file for stylelint, maybe we can check the scripts version and conditionally load the correct rules… I can try that out in repo-tools this week.