Disable ssl_session_tickets which is not supported in older nginx
diff --git a/nginx/files/_ssl_secure.conf b/nginx/files/_ssl_secure.conf
index ec14d47..b23bad0 100644
--- a/nginx/files/_ssl_secure.conf
+++ b/nginx/files/_ssl_secure.conf
@@ -6,6 +6,5 @@
 ssl_dhparam /etc/ssl/dhparams.pem;
 
 ssl_session_cache shared:SSL:10m;
-ssl_session_tickets off;
 ssl_stapling on;
 ssl_stapling_verify on;