Remove SSLv3 from nginx

The default enables SSL v3. This is probably a bad thing.

https://github.com/jfryman/puppet-nginx/blob/v0.0.9/manifests/resource/vhost.pp#L53-L54

By doing this, we prevent people running IE6 on WinXP from accessing our
service. Unfortunately, security concerns mean that we need to make this
change.