NPM's package.json has an extra slash in the tarball url

Problem description:

When uploading an npm package to a local npm repository the pacakge.json that is generated contains an extra slash in the tarball URL.

What is the expected behavior?**

**The package.json's tarball's URL should not contain an extra slash (i.e. before the repository name, npm-local).

Steps to reproduce: ** 

1. Have an npm project. (I used the one from https://github.com/jfrog/project-examples as an example for this issue.)
2. Have a build publish it to an npm local repository
3. Navigate to the local repository and view its package.json
4. Observe the extra slash in the tarball URL

Possible workaround:**

Manually going into every package.json and editing it.

Was that reproduced on GCP machine/mill? yes**