Fix syntax error on Rocky Linux version check (#1182)

Co-authored-by: David Salbei <david@incolab.fr>

openvpn-install.sh

@@ -57,7 +57,7 @@ function checkOS() {
 		fi
 		if [[ $ID == "centos" || $ID == "rocky" || $ID == "almalinux" ]]; then
 			OS="centos"
-			if [[ $VERSION_ID -lt 7 ]]; then
+			if [[ ${VERSION_ID%.*} -lt 7 ]]; then
 				echo "⚠️ Your version of CentOS is not supported."
 				echo ""
 				echo "The script only support CentOS 7 and CentOS 8."