Update golang.org/x dependencies to their latest tagged versions.

Change-Id: Ic2bcf3369062c735a51a1db5d4674344581425c2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/798640
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>