doc: hide blog content for golang.google.cn
doc: hide blog content for golang.google.cn

/blog redirects to blog.golang.org (currently blocked in China)
unless there is a local checkout of golang.org/x/blog, which is
not possible on App Engine Classic.

Change-Id: Ia695e663c9bebcc6c3bedea324c630299eaad4dc
Reviewed-on: https://go-review.googlesource.com/53051
Reviewed-by: Chris Broadfoot <0c2851a4f8ab4aa5606e69c0757771dd13dbe686@golang.org>

akutz/go,nawawi/go,cloudflare/go,codestation/go,josharian/go,Cofyc/go,josharian/go,golang/go,nawawi/go,polyverse-security/go,Cofyc/go,nawawi/go,CAFxX/go,codestation/go,Cofyc/go,akutz/go,cloudflare/go,codestation/go,nawawi/go,akutz/go,akutz/go,akutz/go,CAFxX/go,CAFxX/go,christopher-henderson/Go,Cofyc/go,josharian/go,polyverse-security/go,CAFxX/go,nawawi/go,polyverse-security/go,golang/go,golang/go,golang/go,CAFxX/go,cloudflare/go,codestation/go,Cofyc/go,Cofyc/go,codestation/go,golang/go,cloudflare/go,cloudflare/go,akutz/go,josharian/go,josharian/go,akutz/go,polyverse-security/go,golang/go,nawawi/go,josharian/go,josharian/go,codestation/go,cloudflare/go,cloudflare/go,polyverse-security/go,akutz/go,CAFxX/go,Cofyc/go,CAFxX/go,codestation/go,polyverse-security/go,polyverse-security/go,polyverse-security/go,josharian/go,Cofyc/go,nawawi/go,CAFxX/go,golang/go,golang/go,cloudflare/go,codestation/go,nawawi/go