doc: make the draft 1.13 release notes expected release date accurate
doc: make the draft 1.13 release notes expected release date accurate

Change-Id: I17148bb2b8021ed305ed0d230675d51c41736a11
GitHub-Last-Rev: 2998d46d10587a850fb36f5784df23b371244479
GitHub-Pull-Request: golang/go#34004
Reviewed-on: https://go-review.googlesource.com/c/go/+/192797
Reviewed-by: Ingo Oeser <bdc560eb56f7ac148b6314b93d9d5d92c0a1a4f6@googlemail.com>
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

nawawi/go,akutz/go,nawawi/go,akutz/go,nawawi/go,akutz/go,cloudflare/go,akutz/go,golang/go,golang/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,cloudflare/go,CAFxX/go,akutz/go,cloudflare/go,CAFxX/go,akutz/go,CAFxX/go,golang/go,nawawi/go,golang/go,golang/go,CAFxX/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,nawawi/go,cloudflare/go,CAFxX/go,nawawi/go,golang/go,akutz/go,cloudflare/go,akutz/go,cloudflare/go