> Modules must be semantically versioned according to semver, usually in the form v(major).(minor).(patch), such as v0.1.0, v1.2.3, or v1.5.0-rc.1. The leading v is required. If using Git, tag released commits with their versions

https://github.com/golang/go/wiki/Modules#modules

(I find this reference exceedingly helpful, and wish it were somewhere more official than the `golang/go` wiki, but c'est la vie)