Upgrade to vite@4

[KiwiKilian]

I had a look at the migration guides for vite@4 and rollup@3:

• https://vitejs.dev/guide/migration.html
• https://rollupjs.org/guide/en/#migration

Only change necessary (as far as I found it) was bumping the node engines field to 14, as rollup requires it.

Closes #19

[zachleat]

Shipping with eleventy-plugin-vite@4.0.0