fix(minion.sls): fix `salt-lint` errors

```bash
Examining salt/minion.sls of type state
[210] Numbers that start with `0` should always be encapsulated in quotation marks
salt/minion.sls:20
    - mode: 0644
```

salt/minion.sls

@@ -17,7 +17,7 @@ download-salt-minion:
     {% endif %}
     - user: root
     - group: wheel
-    - mode: 0644
+    - mode: '0644'
     - unless:
       - test -n "{{ salt_settings.version }}" && '/opt/salt/bin/salt-minion --version=.*{{ salt_settings.version }}.*'
     - require_in: