Fix typo in UFW firewall rules

Replace 'allow 5' with 'allow 53' in UFW rules for VPN setup.

Author: nota9x

src/content/docs/guides/vpn-setup.mdx

@@ -81,7 +81,7 @@ Run these four commands:
 ```sh
 sudo ufw allow OpenSSH
 sudo ufw allow 500,4500/udp
-sudo ufw allow 5
+sudo ufw allow 53
 sudo ufw enable
 ```