Fix log message when client disconnects

paircd/server.py

@@ -41,7 +41,7 @@ class Server:
         if client.closed:
             return
 
-        client.log("is quitting: {quit_msg}")
+        client.log(f"is quitting: {quit_msg}")
         msg = QUIT(quit_msg, prefix=client.id())
         for client in self.clients_by_nick.values():
             if client.nickname == nick: