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？
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