design/14951: fix wrong issue link
design/14951: fix wrong issue link

Change-Id: I054a71b08fabb60db7d334735ceabeb6bde3f604
Reviewed-on: https://go-review.googlesource.com/123195
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/proposal,golang/proposal