Adding more nginx SSL parameters 

I am currently using your module to install a GitLab repo within our network.

As I wanted to optimize the SSL config of omnibus embedded nginx to match current standards and easily adopt changes on new SSL/TLS threats, I added some class parameters passed down to the gitlab.rb template.

I did not define any checks, as the implemented changes are just minor and optional. It should not break any existing installations.

(Fixed some small doc issues in the init.pp, too...)

Hope this is usefull for someone else, too. Would be glad if you merge this.