http2/h2demo: Update some links left dangling after the bradfitz/http2 -> x/net/http2 move.
http2/h2demo: Update some links left dangling after the bradfitz/http2 -> x/net/http2 move.

Change-Id: Idd45c1be493f4535d73323fc2feda5efff45763e
Reviewed-on: https://go-review.googlesource.com/15243
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

cmars/tools,DramaFever/golang.org-x-net,cmars/tools,cmars/tools,cesanta/goxnet,albertjin/golang-net,albertjin/golang-net,cmars/tools,cesanta/goxnet,golang/net,DramaFever/golang.org-x-net