cron - redirect stdout to /dev/null to avoid receiving useless emails

tasks/install.yml

@@ -45,4 +45,4 @@
     minute: "{{ backup_cron_minute | default('0') }}"
     hour: "{{ backup_cron_hour | default('2') }}"
     user: root
-    job: "bash /usr/local/bin/brain_backup"
+    job: "bash /usr/local/bin/brain_backup > /dev/null"