fix(syslog_ng.sls): fix `yamllint` errors in test pillar

https://travis-ci.com/saltstack-formulas/syslog-ng-formula/builds/129135816#L210-L217:

```bash
$ yamllint -s .
./test/salt/pillar/syslog_ng.sls
  4:24      warning  truthy value should be one of [false, true]  (truthy)
  6:16      warning  truthy value should be one of [false, true]  (truthy)
  7:17      warning  truthy value should be one of [false, true]  (truthy)
  16:7      error    wrong indentation: expected 8 but found 6  (indentation)
  20:7      error    wrong indentation: expected 8 but found 6  (indentation)
  25:7      error    wrong indentation: expected 8 but found 6  (indentation)
```

test/salt/pillar/syslog_ng.sls

+# -*- coding: utf-8 -*-
+# vim: ft=yaml
 ---
 syslog_ng:
   options:
-    - chain_hostnames: no
+    - chain_hostnames: false
     - flush_lines: 0
-    - use_dns: no
-    - use_fqdn: no
+    - use_dns: false
+    - use_fqdn: false
     - owner: root
     - group: adm
     - perm: =0640
 
   source:
     - s_src:
-      - internal: null
+        - internal: null
 
   destination:
     - d_syslog:
-      - file:
-          - /var/log/syslog
+        - file:
+            - /var/log/syslog
 
   filter:
     - f_syslog3:
-      - =not level(debug)
+        - =not level(debug)
 
   log:
     -