code: func (sv SupportedVersions) NextVersion(current *EtcdVersion) *EtcdVersion {
  	var nextVersion *EtcdVersion
  	for i, supportedVersion := range sv {
  		if current.MajorMinorEquals(supportedVersion) && len(sv) > i+1 {
  			nextVersion = sv[i+1]
  		}
  	}
  	return nextVersion
  }
docs: // NextVersion returns the next supported version after the given current version, or nil if no
  // next version exists.