Fixed a minor nginx warning.

And re-indented the template.

templates/gitea.j2

@@ -2,7 +2,8 @@
 
 {% if gitea_enable_https | default(false) %}
 server {
-    listen 443 ssl http2;
+  listen 443 ssl;
+  http2 on;
   server_name {{ gitea_domain }};
 
   ssl_certificate     {{ gitea_ssl_cert }};