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 $tls_port {
     ~\bacme-tls/1\b 10443;
     default 443;
@@ -27,7 +26,6 @@ stream {
     proxy_pass 10.13.37.42:$tls_port;
     ssl_preread on;
   }
-  }
 }
 ```