cmd/go: update comment to not say GO386 does not exist
GO386 was removed by CL 258957, but it was restored by CL 260017.
Change-Id: Iced49ca61512a0f2ef513acbf9700a87ac964c68
Reviewed-on: https://go-review.googlesource.com/c/go/+/580675
Auto-Submit: Ian Lance Taylor <iant@golang.org> Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Keith Randall <khr@golang.org>