godoc: avoid exposing absolute paths on 404

Exposing the full paths to files is considered possible
source of vulnerabilities.

Change-Id: Ie9ae3791e51fcff5f1df711f84db9879d7e6ce37
Reviewed-on: https://go-review.googlesource.com/29445
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed