The release process

Before starting, make sure that you configured version prefix to be v during running git flow init. You can do that by checking your git config (cat .git/config | grep -A 7 prefix) If you don't see versiontag = v. Configure git flow init -f again.
Start a release with git flow release start <new version>
Manually bump up package version (using semantic versioning) in both package.json and package-lock.json and commit.
Push the release branch and create a new MR
Finish the release with git flow release finish <new version>
Push develop master branches and git push --tags.
Manually run the deploy step on the tag pipeline.
check out the v<version> tag and run npm publish to upload the module to https://www.npmjs.com/package/gitter-sidecar

Validate the release

go to https://sidecar.gitter.im/ and check that the downloaded sidecar.v1.js is in the new version (using Dev Tools)
see the new version published in npm repository https://www.npmjs.com/package/gitter-sidecar