Add quotes around kernel_shmax to keep it an integer

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

ansible/roles/postgresql_server/tasks/main.yml

@@ -56,7 +56,7 @@
   - postgresql
 
 - name: Set kernel shared memory max to a larger value
-  sysctl: name=kernel.shmmax value={{ kernel_shmmax }}
+  sysctl: name=kernel.shmmax value="{{ kernel_shmmax }}"
   when: kernel_shmmax is defined
   notify:
   - restart postgresql