学习go语言圣经遇到的问题

1.5节fetch.go的例子 输入 go build gopl.io/ch1/fetch之后 遇到如下问题

can't load package: package gopl.io/fetch: cannot find package "gopl.io/fetch" in any of: D:\Go\src\gopl.io\fetch (from $GOROOT) D:\Go\MyGoProject\src\gopl.io\fetch (from $GOPATH)

请问该如何解决