net/http/fcgi: update URL to spec documentation
net/http/fcgi: update URL to spec documentation

Fixes #23748

Change-Id: Iacdbd57c53492175cf1d3045640db61151e10731
Reviewed-on: https://go-review.googlesource.com/92955
Reviewed-by: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>

Cofyc/go,akutz/go,akutz/go,codestation/go,golang/go,CAFxX/go,CAFxX/go,nawawi/go,codestation/go,Cofyc/go,nawawi/go,akutz/go,josharian/go,golang/go,Cofyc/go,Cofyc/go,cloudflare/go,codestation/go,cloudflare/go,cloudflare/go,cloudflare/go,Cofyc/go,cloudflare/go,codestation/go,josharian/go,CAFxX/go,nawawi/go,CAFxX/go,codestation/go,CAFxX/go,golang/go,josharian/go,codestation/go,Cofyc/go,CAFxX/go,codestation/go,cloudflare/go,josharian/go,akutz/go,nawawi/go,cloudflare/go,Cofyc/go,CAFxX/go,CAFxX/go,josharian/go,cloudflare/go,nawawi/go,akutz/go,golang/go,josharian/go,josharian/go,josharian/go,akutz/go,golang/go,nawawi/go,codestation/go,nawawi/go,Cofyc/go,nawawi/go,golang/go,akutz/go,golang/go,akutz/go,golang/go