Tag unreleased package's definition as next on npm registry

[ikatyang]

For example: @types/gulp is now versioned v4.x with latest tag, but the gulp package itself is just versioned v3.x with latest tag, the gulp v4.x is even not published on npm yet, it's just a 4.0 branch on its GitHub repo.

Can we consider a pre-release comment (e.g. // Pre-release: true) to mark this definition as next tag to publish on npm? So that we don't have to specify version manually and can be handled by other auto-updating tools like Greenkeeper.