npm 5 introduced package-lock.json, of which the documentation is here.
It states that the file is intended to be included with version control, so anyone cloning your package and installing it will have the same dependency versions. In other words, you should not add it to your .gitignore file.
What it does not state is wether or not the file is intended to be included with a published package. This question could be rephrased as; should package-lock.json be included in .npmignore?
It cannot be published.
From the npm documentation:
One key detail about package-lock.json is that it cannot be published, and it will be ignored if found in any place other than the toplevel package
See package-lock.json documentation on docs.npmjs.com.
However, you should be commiting your package-lock.json
to git as per the documentation.
This file is intended to be committed into source repositories
hence the common message presented by npm:
created a lockfile as package-lock.json. You should commit this file.
EDIT: A more detailed explanation can be found here.