Allow multiple get_query_string calls

Author: trungleduc

voila/query_parameters_handler.py

@@ -57,5 +57,5 @@ def send_updates(cls: 'QueryStringSocketHandler', msg: Dict) -> None:
                 waiter.write_message(payload)
             except Exception:
                 logging.error("Error sending message", exc_info=True)
-        else:
-            cls._cache[kernel_id] = payload
+
+        cls._cache[kernel_id] = payload