upgrade devDependencies

[benmccann]

These are simply major version upgrades to keep the library using modern tooling in its testing setup.

This has no effect on consumers of the library since it updates devDependencies, which only affects developers of this library (and the CI). Consumers of the library are only affected by changes to the dependencies in package.json

There were a couple I left out because they would be more complicated and would be better to handle separately. codecov has been deprecated and replaced with a GitHub action. The eslint upgrade requires updating the config file, but first the common mapbox config must be updated.

[benmccann]

@lukekarrys could I ask for a quick peek at this one?

[benmccann]

@cclauss would you be able to take a look at this PR?

[lukekarrys]

Apologies for going MIA on this repo and my responsibilities I promised to take on. My goal is to take a look at everything this weekend, and I have carved on time to do so! 🙌🏼

[cclauss]

I know the feeling. I have the same issues as you on several Python repos. It is difficult to do the day job and then also do this volunteer work. This is especially true during beautiful summer daze in the gorgeous Swiss Alps!

Thanks massively for your efforts. I am delighted that you have the skills that I lack and are willing to dedicate some time to getting this project back on track.

[benmccann]

Thanks @lukekarrys!

[benmccann]

@lukekarrys I thought I'd check back in and see if you might have a chance to lend a pair of eyes to this now?