Use ntp (instead of systemd-timesyncd) on Ubuntu 18.04

Seems like Ubuntu 18.04 does not have a dedicated `systemd-timesyncd` package, nor
does it include the `systemd-timesyncd` binary in the main `systemd` package.

Fixes spantaleev#1302

Regression since spantaleev#1192

Author: spantaleev

roles/matrix-base/defaults/main.yml

@@ -83,8 +83,8 @@ matrix_host_command_openssl: "/usr/bin/env openssl"
 matrix_host_command_systemctl: "/usr/bin/env systemctl"
 matrix_host_command_sh: "/usr/bin/env sh"
 
-matrix_ntpd_package: "{{ 'systemd-timesyncd' if (ansible_distribution == 'CentOS' and ansible_distribution_major_version > '7') or (ansible_distribution == 'Ubuntu' and ansible_distribution_major_version > '16') else 'ntp' }}"
-matrix_ntpd_service: "{{ 'systemd-timesyncd' if (ansible_distribution == 'CentOS' and ansible_distribution_major_version > '7') or (ansible_distribution == 'Ubuntu' and ansible_distribution_major_version > '16') or ansible_distribution == 'Archlinux' else ('ntpd' if ansible_os_family == 'RedHat' else 'ntp') }}"
+matrix_ntpd_package: "{{ 'systemd-timesyncd' if (ansible_distribution == 'CentOS' and ansible_distribution_major_version > '7') or (ansible_distribution == 'Ubuntu' and ansible_distribution_major_version > '18') else 'ntp' }}"
+matrix_ntpd_service: "{{ 'systemd-timesyncd' if (ansible_distribution == 'CentOS' and ansible_distribution_major_version > '7') or (ansible_distribution == 'Ubuntu' and ansible_distribution_major_version > '18') or ansible_distribution == 'Archlinux' else ('ntpd' if ansible_os_family == 'RedHat' else 'ntp') }}"
 
 matrix_homeserver_url: "https://{{ matrix_server_fqn_matrix }}"