fix unbound variable

update-gluon.sh

@@ -13,7 +13,7 @@ upstream_newest_minor=$(git ls-remote --tags --refs https://github.com/freifunk-
 fork_newest_minor_branch="$upstream_newest_minor-ffs"
 fork_newest_minor_tag="$upstream_newest_minor-ffs0.1"
 
-git clone "$gluon_git_url" gluon
+git clone "$gluon_upstream_git_url" gluon
 cd gluon
 git remote add upstream "$gluon_upstream_git_url"
 git fetch upstream --tags