add dist-tag to Jenkinsfile-based `npm publish ...` for non-current-major releases

[trentm]

We are currently adding support for CI-based npm publish ... on new vX.Y.Z version tags. When we do a new major (4.x) and may then have new maintenance releases of the previous major (3.x), then we need to make sure that the npm publish becomes npm publish --tag 3x. Otherwise a 3.x release will be incorrectly npm-dist-tagged with "latest".