Fix permission on sudoers file

Change-Id: Ieaf51fb60cd601d7831008197724b13b7e3beaad
diff --git a/tasks/main.yml b/tasks/main.yml
index 35237bc..6a57595 100644
--- a/tasks/main.yml
+++ b/tasks/main.yml
@@ -30,7 +30,7 @@
     dest: "/etc/sudoers.d/acme_sudoers"
     owner: "root"
     group: "root"
-    mode: 0644
+    mode: 0440
     validate: "visudo -c -s -f %s"
 
 - name: Create certificate dir