Add http → https redirect in nginx SSL example config

Test cases:

```sh
$ curl -I -k http://www.example.com
HTTP/1.1 301 Moved Permanently
Server: nginx/0.7.67
Date: Thu, 21 Aug 2014 12:08:18 GMT
Content-Type: text/html
Content-Length: 185
Connection: keep-alive
Location: https://www.example.com/

$ curl -I -k https://www.example.com
HTTP/1.1 200 OK
Server: nginx
Date: Thu, 21 Aug 2014 12:10:54 GMT
Content-Type: text/html; charset=utf-8
Connection: keep-alive
Vary: Cookie
ETag: "7ee74e2ad31e0e27becec0f386546a70"
X-UA-Compatible: IE=Edge,chrome=1
X-Runtime: 0.122378
X-Request-Id: 391bb16391e86c5597e9c26bcb9081eb
Cache-Control: max-age=3600, public
Strict-Transport-Security: max-age=31536000
```