cmd/gitmirror: add vgo repo to mirror whitelist
cmd/gitmirror: add vgo repo to mirror whitelist

Fixes golang/go#23945

Change-Id: Ifbae9d09c6d91fb392e0ebbda35995e668d99f22
Reviewed-on: https://go-review.googlesource.com/95499
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

golang/build,golang/build,golang/build,golang/build