vcs_update: improve the case when it's run without arguments

Signed-off-by: Alejandro Mery <amery@geeks.cl>

files/bin/vcs_update

@@ -38,7 +38,13 @@ update_repo() {
 	cd - > /dev/null
 }
 
-[ $# -gt 0 ] || set -- .
+if [ $# -eq 0 ]; then
+	if git rev-parse --is-inside-work-tree > /dev/null; then
+		set -- "$(git rev-parse --show-toplevel)"
+	else
+		set -- .
+	fi
+fi
 
 for d; do
 	if [ -e "$d/.git" ]; then