code: func (p *Project) RollbackVersion(version string) error {
  	p.Log.Debugf("rolling back %d functions to version %s", len(p.Functions), version)
  
  	for _, fn := range p.Functions {
  		if err := fn.RollbackVersion(version); err != nil {
  			return fmt.Errorf("function %s: %s", fn.Name, err)
  		}
  	}
  
  	return nil
  }
docs: // RollbackVersion project functions to the specified version.