(fix) Missing apache config for sub-dir multisites
(fix) Missing apache config for sub-dir multisites

Because:

* `whippet server` appears to be ignoring the multisite redirect config
  in `/etc/apache2/sites-enabled/wordpress.conf`.
* Requests to theme assets within multisite paths are returning `404`s,
  however requests to the same assets on the root site are returning
  `200`s.
* See #107 for details.

This change:

* Sets the `<Directory>` path to `/var/www/html/`.
* This is more specific, but should introduce any issues as the docroot
  for the only site within the container is `/var/www/html`.

Fixes #107

dxw/whippet,dxw/whippet,dxw/whippet