#804 Fix updater php package retrieving

Updater script retrieves php7.1-mapi package instead of php7.2 metapackage.
Otherwise, updating from 1.1.1c to 1.2.0 fails.

This commit changes "apt-cache" search for the "php7.2" specific package
dependency which is available in Ubuntu 18.04.

installer/opengnsys_update.sh

@@ -428,7 +428,7 @@ function installDependencies()
 	eval $UPDATEPKGLIST
 	if [ -f /etc/debian_version ]; then
 		# Basado en paquetes Deb.
-		PHP7VERSION=$(apt-cache pkgnames php7 2>/dev/null | sort | head -1)
+		PHP7VERSION="php7.2"
 		PHPFPMSERV="${PHP7VERSION}-fpm"
 		PHP5PKGS=( $(dpkg -l | awk '$2~/^php5/ {print $2}') )
 		if [ -n "$PHP5PKGS" ]; then