declare language for nginx config snippet

content/en/docs/install/fresh.md

@@ -333,7 +333,7 @@ You may clear NGINX's cache by manually deleting the cache directory
   sure. When you've found the directive, the cache directory will be
   listed in the first parameter. Here's an example:
 
-  ```
+  ```nginx
   # Here, the cache directory is "/var/cache/nginx".
   proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=cache1:16m max_size=1g inactive=720m use_temp_path=off;
   ```