Predictable updates of yarn version

[daveisfera]

When the yarn version changes, it means that a new base image is generated. Can this be limited to a predictable schedule? I was thinking that update to the latest stable version of yarn when a new point release is made.

[razor-x]

See also #386 (comment)

[Starefossen]

Yarn will continued to be updated when Node.js version are updated. However, since Yarn is still experimental and has not reached a stable version (eg. 1.0) there may be breaking changes. Use on own risk.

[daveisfera]

If this is really the stance being taken, then I believe that there should be a separate tag for the builds that include yarn. Having the image change every time yarn decides to do a release breaks the concept of fixed/reproducible builds in Docker.

[nschonni]

Think this is answered in the CONTRIBUTING.md now

Yarn is updated to the latest version only when there is a new Node.js SemVer-minor release, and it's updated only in the branch with the new release, preferably in the same PR. The update.sh script does this automatically when invoked with a specific branch, e.g. ./update.sh 6.10.

[pesho]

Yes, @nschonni is right. This was resolved in #393