Fix use of variable in translation platform script

Bug introduced in: 107adf3e

files/weblate/scripts/update-staging-website.sh

@@ -14,7 +14,7 @@ IKIWIKI_LOGFILE=/var/log/weblate/update-staging-website_ikiwiki.log
 
 /var/lib/weblate/scripts/save-suggestions.py "$STAGING_REPO_DIR"
 
-cd "STAGING_REPO_DIR"
+cd "$STAGING_REPO_DIR"
 
 # Note: cron ignores the exit code so on errors, we print a message to
 # STDERR, which cron will then send over email