[auto-install] Fix case sensitivity for OpenVPN disable option #490

Replace bash 4.0+ specific ${var,,} syntax with explicit case checking
to ensure compatibility with older bash versions (3.x). Now accepts
both 'N' and 'n' to disable OpenVPN module as advertised in the prompt.

Fixes issue where users entering uppercase 'N' (as instructed) would
not disable the OpenVPN module on systems with bash < 4.0.

Author: Adityashandilya555

deploy/auto-install.sh

@@ -148,7 +148,7 @@ setup_docker_openwisp() {
 		# VPN domain
 		if [[ -z "$vpn_domain" ]]; then
 			set_env "VPN_DOMAIN" "openvpn.${domain}"
-		elif [[ "${vpn_domain,,}" == "n" ]]; then
+		elif [[ "$vpn_domain" == "n" || "$vpn_domain" == "N" ]]; then
 			set_env "VPN_DOMAIN" ""
 		else
 			set_env "VPN_DOMAIN" "$vpn_domain"