chore: updating dependencies and node versions

* Updated supported Node.js versions

Dropped support for 14 and 16 in favor of the current LTS versions 18
and 20.

* Updated Node.js dependencies

Bumped nearly all dependencies to the latest. The exception being
`node-fetch` which made the jump to using ESM which is still causing
folks a lot of grief.

* Shored code coverage back up to 100%

Had some remnants from when this library did sanity checks pre-flight to
the API that required additional tests to cover them, or just adjusting
the argument defaults.

* Removed the "build" badge from the README

Seems there were some gotchas with that badge that makes it kind of a
pain, as it has to be hard coded a certain way. I messed with it and
couldn't get it working, seems like more trouble than it's worth.

Further details: https://github.com/badges/shields/issues/8671

* Added .nvmrc file

Pretty self explanatory.

* Bumped version number

Lucky number 7, y'all!

README.md

@@ -2,7 +2,6 @@
 
 [![License](https://img.shields.io/npm/l/holidayapi-node?style=for-the-badge)](https://github.com/holidayapi/holidayapi-node/blob/master/LICENSE)
 ![Node Version](https://img.shields.io/node/v/holidayapi?style=for-the-badge)
-[![Test Status](https://img.shields.io/github/workflow/status/holidayapi/holidayapi-node/Test?style=for-the-badge)](https://github.com/holidayapi/holidayapi-node/actions)
 [![Code Coverage](https://img.shields.io/codecov/c/github/holidayapi/holidayapi-node?style=for-the-badge)](https://codecov.io/gh/holidayapi/holidayapi-node)
 
 Official Node.js library for [Holiday API](https://holidayapi.com) providing