Add a mising closing curly brace (#1588)

in *Unique IDs* section, the `strings.json` example require one more closing curly brace to be valid json

docs/config_entries_config_flow_handler.md

@@ -80,6 +80,7 @@ Should the config flow then abort, the text resource with the key `already_confi
       "already_configured": "Device is already configured"
     }
   }
+}
 ```
 
 By setting a unique ID, users will have the option to ignore the discovery of your config entry. That way, they won't be bothered about it anymore.