Cron addition

https://github.com/alexbelgium/hassio-addons/issues/435

transmission_openvpn/Dockerfile

@@ -55,7 +55,7 @@ RUN if ! command -v bash >/dev/null 2>/dev/null; then (apt-get update && apt-get
     && chmod -R 755 /etc/cont-init.d || printf '%s\n' "${MODULES}" >/MODULESFILE
 
 # Manual apps
-ENV PACKAGES="nginx"
+ENV PACKAGES="nginx cron"
 
 # Automatic apps & bashio
 # hadolint ignore=SC2015