Copy package-lock.json too

[j-frost]

Currently, AppEngine complains during upload:

Updating service [default]...⠶WARNING: *** Improve build performance by generating and committing package-lock.json.

If this is not some kind of config error on my part, I'll be happy to submit a PR for this.

[HalfdanJ]

It's not on your part. It is a warning, but i've been ignoring it since I don't think it actually has any meaningful impact in this case, since very few dependencies are actually installed in appengine.

[novakma2]

It seems to be good practice probably, gets rid of warning and does no harm probably 🤔