cmd/godoc: fix command for creating the zip file

The `-r` option (to recurse into directories) need to be specified
else the created file consists only of the specified directory and
nothing else.

Change-Id: I624184fc2e88998a3119c12f8c328603588c123c
Reviewed-on: https://go-review.googlesource.com/17283
Reviewed-by: Russ Cox <rsc@golang.org>
1 file changed