Update config.yml.example

Due to trouble with SSLv3, supported ssl ciphers need to be listed explicit.

I suggest add to file `config.yml.example` following line

    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;

More info about nginx security: https://raymii.org/s/tutorials/Strong_SSL_Security_On_nginx.html

See pull request