安装golang tour，提示错误

试图在自己机器上安装golang tour，出现了问题。

Couldn't find tour files: could not find go-tour content; check $GOROOT and $GOPATH

请教一下各位前辈如何解决。上网找了几天，没有找到答案。谢谢先~

系统环境是这样的：

export GOROOT=/usr/local/go

export GOPATH=/usr/local/GOPATH

export PATH=$PATH:$GOROOT/bin:$GOPATH/bin

export GO111MODULE=on

安装步骤：

~# go get golang.org/x/tour

go: finding golang.org/x/tour latest

go: finding golang.org/x/tools v0.0.0-20190312164927-7b79afddac43

go: finding golang.org/x/net v0.0.0-20190311183353-d8887717615a

go: finding golang.org/x/text v0.3.0

go: finding golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2

go: finding golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a

go: downloading golang.org/x/tour v0.0.0-20190611164551-1f1f3d2b450b

go: extracting golang.org/x/tour v0.0.0-20190611164551-1f1f3d2b450b

go: downloading golang.org/x/tools v0.0.0-20190312164927-7b79afddac43

go: extracting golang.org/x/tools v0.0.0-20190312164927-7b79afddac43

go: downloading golang.org/x/net v0.0.0-20190311183353-d8887717615a

go: extracting golang.org/x/net v0.0.0-20190311183353-d8887717615a

运行：

~# tour

2019/06/17 16:00:33 Couldn't find tour files: could not find go-tour content; check $GOROOT and $GOPATH

我想请教的问题：

1、这个错误怎么修正？

2、试图go mod download安装到其它目录（学习go mod），发现还是下载到$GOPATH/pkg中

正确的操作方法是什么呢？