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

```bash
Examining nginx/certificates.sls of type state
[206] Jinja variables should have spaces before and after: {{ var_name }}
nginx/certificates.sls:40
    - contents_pillar: {{salt['pillar.get']('nginx:certificates:{}:public_cert_pillar'.format(domain))}}

[202] Jinja statement should have spaces before and after: {% statement %}
nginx/certificates.sls:47
{% if salt['pillar.get']("nginx:certificates:{}:private_key".format(domain)) or salt['pillar.get']("nginx:certificates:{}:private_key_pillar".format(domain))%}

[206] Jinja variables should have spaces before and after: {{ var_name }}
nginx/certificates.sls:54
    - contents_pillar: {{salt['pillar.get']('nginx:certificates:{}:private_key_pillar'.format(domain))}}
```

nginx/certificates.sls

@@ -37,21 +37,21 @@ nginx_{{ domain }}_ssl_certificate:
     - name: {{ certificates_path }}/{{ domain }}.crt
     - makedirs: True
 {% if salt['pillar.get']("nginx:certificates:{}:public_cert_pillar".format(domain)) %}
-    - contents_pillar: {{salt['pillar.get']('nginx:certificates:{}:public_cert_pillar'.format(domain))}}
+    - contents_pillar: {{ salt['pillar.get']('nginx:certificates:{}:public_cert_pillar'.format(domain)) }}
 {% else %}
     - contents_pillar: nginx:certificates:{{ domain }}:public_cert
 {% endif %}
     - watch_in:
       - service: nginx_service
 
-{% if salt['pillar.get']("nginx:certificates:{}:private_key".format(domain)) or salt['pillar.get']("nginx:certificates:{}:private_key_pillar".format(domain))%}
+{% if salt['pillar.get']("nginx:certificates:{}:private_key".format(domain)) or salt['pillar.get']("nginx:certificates:{}:private_key_pillar".format(domain)) %}
 nginx_{{ domain }}_ssl_key:
   file.managed:
     - name: {{ certificates_path }}/{{ domain }}.key
     - mode: 600
     - makedirs: True
 {% if salt['pillar.get']("nginx:certificates:{}:private_key_pillar".format(domain)) %}
-    - contents_pillar: {{salt['pillar.get']('nginx:certificates:{}:private_key_pillar'.format(domain))}}
+    - contents_pillar: {{ salt['pillar.get']('nginx:certificates:{}:private_key_pillar'.format(domain)) }}
 {% else %}
     - contents_pillar: nginx:certificates:{{ domain }}:private_key
 {% endif %}