go clean -cache

go 構建時會產生很多緩存， 一般是目錄：/Users/xxx/Library/Caches/go-build

此目錄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.
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