Do I need to publish to npm every time I update a package available via git?

Travis CI can publish to npm when you push a version tag to reduce the overhead of releasing a change. Enable in your .travis.yml with:

deploy: 
  provider: npm
  api_key: "YOUR API KEY"
  on:
    - tags: true

Check the travis docs for details. There’s also a step-by-step guide in this post.