References to the gallery feed URL need updating to the new URL

[robertwray]

There are several places in the documentation that refer to the old gallery feed (http://packages.orchardproject.net/FeedService.svc) instead of the new gallery feed (https://gallery.orchardproject.net/api/FeedService):

• docs/Documentation/Gallery-Overview.markdown
• docs/Documentation/Module-gallery-feeds.markdown
• docs/Documentation/Packaging-and-sharing-a-module.markdown