demo redirect

site/redirects.json

@@ -6,6 +6,7 @@
   { "source": "/docs/index", "destination": "/docs/getting-started", "permanent": true },
   { "source": "/licence", "destination": "/license", "permanent": true },
   { "source": "/documentation", "destination": "/docs", "permanent": true },
+  { "source": "/demo", "destination": "https://preview.tabler.io", "permanent": true },
   {
     "source": "/:name(emails|emails/gallery|gallery|terms-of-service|privacy-policy|license?).html",
     "destination": "/:name",