[release-branch.go1.16] cmd: upgrade golang.org/x/mod to fix go.mod parser
modfile.Parse passed an empty string to the VersionFixer for the
module path. This caused errors for v2+ versions.
For #44496
Change-Id: I13b86b6ecf6815c4bc9a96ec0668284c9228c205
Reviewed-on: https://go-review.googlesource.com/c/go/+/296131
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
(cherry picked from commit
bcac57f89c0ec609e6fbebcbcd42bb73fdaef2f0)
Reviewed-on: https://go-review.googlesource.com/c/go/+/297990
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>