捆绑软件：在当前目录中找不到软件包：PWD中没有可构建的Go源文件

Using the go bundle too located here:

https://godoc.org/golang.org/x/tools/cmd/bundle

I try running:

bundle -o bun ./builds/one

and I get this error:

bundle: cannot find package in current directory: no buildable Go source files in $PWD

Why is the tool not understanding that I want to search for go files in

$PWD/builds/one

not

$PWD

?

I tried using an absolute path instead of relative path, same problem. The directory looks like:

$PWD/
  builds/
      one/
        bar/
          bar.go
        foo/
          foo.go
        one.go

maybe I need to set $GOPATH or $GOROOT? I tried setting those, same problem.