Overwrites existing build.rollupOptions.external

[jordan-meraki]

Using the plugin as is overwrites existing build.rollupOptions.external.

It appears that this is because it returns a function instead of an array which isn't merge-able.

I'd recommend updating the readme to mention that if you already have an external array, you can just move its contents to include within the externalizeDeps argument.

[szszoke]

This also happens when the plugin is used twice in the same configuration. My use case for that is to externalize dependencies in an NPM workspace like this:

externalizeDeps({
  useFile: '../../package.json',
}),
externalizeDeps({
})