[borgbackups] Make use of handlers

roles/borgbackup-client/handlers/main.yml

+---
+- name: restart cron
+  service:
+    name: cron
+    state: restarted

roles/borgbackup-client/tasks/main.yml

@@ -45,4 +45,5 @@
   template:
     src: "cron.d/borg.j2"
     dest: "/etc/cron.d/borg"
+  notify: restart cron