Allow setting the registry hostname

contrib/update.sh

@@ -24,7 +24,8 @@ trap "rm -f $tmp_file 2>/dev/null" EXIT
 gitlab-deps list-projects $opts \
     | egrep "${PROJECT_REGEXP:-.*}" \
     | gitlab-deps deps $opts \
-                  > $tmp_file
+        ${GITLAB_REGISTRY_HOSTNAME:+--registry=${GITLAB_REGISTRY_HOSTNAME}} \
+        > $tmp_file
 
 if ! cmp --quiet $tmp_file $deps_file; then
     mv -f $tmp_file $deps_file

debian/gitlab-deps.default

 # Set to the public URL of your Gitlab repository.
 GITLAB_URL=
 
+# Set to the registry hostname (https:// is assumed) if necessary.
+GITLAB_REGISTRY_HOSTNAME=
+
 # File with the authorization token.
 GITLAB_TOKEN_FILE=/var/lib/gitlab-deps/auth_token