go clean -cache

go 构建时会产生很多缓存， 一般是目录：/Users/xxx/Library/Caches/go-build

此目录README：

This directory holds cached build artifacts from the Go build system.
Run "go clean -cache" if the directory is getting too large.
Run "go clean -fuzzcache" to delete the fuzz cache.
See golang.org to learn more about Go.