update ssl_ciphers

taken from
https://raymii.org/s/tutorials/Strong_SSL_Security_On_nginx.html /
https://cipherli.st/

backwards compatible ciphers not needed since gitlab does not support
ie8

lib/support/nginx/gitlab-ssl

@@ -76,7 +76,7 @@ server {
   ssl_certificate /etc/nginx/ssl/gitlab.crt;
   ssl_certificate_key /etc/nginx/ssl/gitlab.key;
 
-  ssl_ciphers 'ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA256:ECDHE-RSA-AES256-SHA:ECDHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES256-GCM-SHA384:AES128-GCM-SHA256:AES256-SHA256:AES128-SHA256:AES256-SHA:AES128-SHA:DES-CBC3-SHA:HIGH:!aNULL:!eNULL:!EXPORT:!CAMELLIA:!DES:!MD5:!PSK:!RC4';
+  ssl_ciphers 'AES256+EECDH:AES256+EDH';
 
   ssl_protocols  TLSv1 TLSv1.1 TLSv1.2;
   ssl_session_cache  builtin:1000  shared:SSL:10m;