Fix Ansible 2.8 warning (#218)

See https://docs.ansible.com/ansible/latest/porting_guides/porting_guide_2.8.html#module-option-conversion-to-string

tasks/install.yml

@@ -2,7 +2,7 @@
 - name: enable overcommit in sysctl
   sysctl:
     name: vm.overcommit_memory
-    value: 1
+    value: "1"
     state: present
     reload: yes
     ignoreerrors: yes