Consider revising node 18 requirement

Users of Debian 11 (stable) don't have access to Node 18 from system packages, only Node 17.2:
```
npm WARN EBADENGINE Unsupported engine {
npm WARN EBADENGINE package: 'jsvu@2.0.1',
npm WARN EBADENGINE required: { node: '>=18.0.0' },
npm WARN EBADENGINE current: { node: 'v17.2.0', npm: '8.19.2' }
npm WARN EBADENGINE }
```
While 18 is LTS it might make sense to keep the requirement at 17.x until both debian and ubuntu have it, unless there's some specific reason why jsvu is complex enough to need 18. I'm still able to use the current version of jsvu to update v8, but we also have some CI machines on older distributions that are unable to use jsvu at all due to the increased requirements. Maybe there's something I don't understand about jsvu that explains why it needs a node release from 10 months ago.
Thanks!