Add HTTPS support to Nginx config

If we don't include the port number in Host,
Rack::Protection::HttpOrigin kicks in and our session is cleared.

Reference:

https://github.com/rkh/rack-protection/blob/master/lib/rack/protection/http_origin.rb

From http://wiki.nginx.org/HttpCoreModule#.24host

    This variable is equal to line Host in the header of request or name
    of the server processing the request if the Host header is not
    available.

    This variable may have a different value from $http_host in such
    cases: 1) when the Host input header is absent or has an empty
    value, $host equals to the value of server_name directive; 2)when
    the value of Host contains port number, $host doesn't include that
    port number. $host's value is always lowercase since 0.8.17.

Close #4.

This was originally added in blackgate:

https://github.com/twingly/blackgate/commit/7467f18a69b80909e0c2f056dc2b20f078e085ea
https://github.com/twingly/blackgate/commit/f24187141fa6e7f0a405ab63ef80d8e210441cb6