Update the doc directory to use https://www.wireshark.org.

Change-Id: I9bfc57cb6b6ab6962b80ff58d98eb351d6f69829
Reviewed-on: https://code.wireshark.org/review/4140
Reviewed-by: Gerald Combs <gerald@wireshark.org>
(cherry picked from commit 175039128a10b083bcc20af88531b38709423964)
Reviewed-on: https://code.wireshark.org/review/4155