vhost: add a blank line at the end of the header template

Without it, we get something like this:

```
  error_log             /var/log/nginx/my_error.log;  location / {
    root      /var/www/html;
  }
```

With this commit, we get this:

```
  error_log             /var/log/nginx/my_error.log;

  location / {
    root      /var/www/html;
  }
```
Merge pull request #490 from vincentbernat/fix/blank-line-vhost-header

vhost: add a blank line at the end of the header template