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

Change-Id: Id3afb41fc96c3eaa63241116bb332d4779e6b5f6
Reviewed-on: https://go-review.googlesource.com/c/net/+/694175
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>