fix tls-alpn-01 configuration example

docs/tls-alpn.md

@@ -15,7 +15,6 @@ Your config should look something like this:
 
 ```nginx
 stream {
-  server {
   map $ssl_preread_alpn_protocols $tls_port {
     ~\bacme-tls/1\b 10443;
     default 443;
@@ -28,7 +27,6 @@ stream {
     ssl_preread on;
   }
 }
-}
 ```
 
 That way https requests are forwarded to port 443 on the backend server, and acme-tls/1 requests are