units: fix condition for systemd-journal-catalog-update.service (systemd#4990)

The service is supposed to regenerate the catalog index whenever /usr is
updated, but /var is not. Hence the ConditionNeedsUpdate= line should
actually reference /var, as that's where the index file is located.

Author: poettering

units/systemd-journal-catalog-update.service.in

@@ -12,7 +12,7 @@ DefaultDependencies=no
 Conflicts=shutdown.target
 After=local-fs.target
 Before=sysinit.target shutdown.target systemd-update-done.service
-ConditionNeedsUpdate=/etc
+ConditionNeedsUpdate=/var
 
 [Service]
 Type=oneshot