code: func environ() (env []string) {
  	for _, v := range os.Environ() {
  		if !strings.HasPrefix(v, "GOPATH=") {
  			env = append(env, v)
  		}
  	}
  	env = append(env, "GOPATH="+gopath)
  	return
  }
docs: // environ returns the original execution environment with GOPATH
  // replaced (or added) with the value of the global var gopath.