fix: fix required versions of Node.js
fix: fix required versions of Node.js

The reason for chosing this semver format is to follow the update made
in `ember-cli` v3.28:

https://github.com/ember-cli/ember-addon-output/blob/v3.28.2/package.json#L70

```
"node": "12.* || 14.* || >= 16"
```

xcambar/ember-cli-embedded,xcambar/ember-cli-embedded