After godoc stopped being part of the Go distribution, the location
of the godoc binary and the go binary can be different. Hence the old
GOROOT finding logic does not work anymore.
We shell out to "go env GOROOT" to return the new GOROOT.
Fixesgolang/go#23445
Change-Id: I16e4c0798e3f5cda13d9f6546cf82808a10c4a0b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/199279
Reviewed-by: Andrew Bonventre <andybons@golang.org>
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>