Automatic application of license header

Author: github-actions[bot]

packages/jupyter-chat/src/message.ts

@@ -1,3 +1,8 @@
+/*
+ * Copyright (c) Jupyter Development Team.
+ * Distributed under the terms of the Modified BSD License.
+ */
+
 import { ISignal, Signal } from '@lumino/signaling';
 import { IAttachment, IMessageContent, IMessage, IUser } from './types';