Cannot publish to local npm registry

[Chriscbr]

If you use a tool like Verdaccio to host a proxy npm registry on your own computer and try setting the environment variable NPM_REGISTRY to localhost:XXXX when invoking publib-npm, the command fails because it tries publishing to https://localhost:4872 instead of http://localhost:4872. Whether or not we connect to the registry over HTTPS should be configurable.