[x/blog] _content: fix broken links in cgo article
[x/blog] _content: fix broken links in cgo article

The correct links to sections on cmd/go page are prefixed with "hdr-".

Change-Id: I8301a8f93c2a6ebbc3d67a9a82c809e776976922
Reviewed-on: https://go-review.googlesource.com/c/blog/+/319470
Trust: Alberto Donizetti <90b16103a35511ced020676f3544f17117fb4c92@gmail.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
X-Blog-Commit: 594fa988c67b77baa1b04aa1ae57dc507f2f8045

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website