Use NPM-standard `publishConfig` instead of `config` to define access level

[jan-molak]

Hi there!

NPM has a standard way of configuring the scoped package's access level and deployment registry.
This is done using the publishConfig key in the package.json, as per the docs.

However, instead of using the publishConfig, lerna-semantic-release relies on the config key instead. This means that even though the publishConfig.access property is specified, lerna-semantic-release ignores it and publishes any scoped package as private.

It would be great if lerna-semantic-release could use the same NPM standard as it would make releasing scoped packages easier.

[junosuarez]

likewise, in lerna-semantic-release-get-last-release, rather than checking for private:true, if publishConfig.registry is set, I think it should use the local version registration.