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

Change-Id: I7f67042b70ae290dc0ca73793ad35882e395e629
Reviewed-on: https://go-review.googlesource.com/c/net/+/798460
Auto-Submit: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>