[AUTOMATED]: License Headers

Author: Feiyang1

packages-exp/firebase-exp/app/index.cdn.ts

@@ -1,3 +1,20 @@
+/**
+ * @license
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 import { registerVersion } from '@firebase/app-exp';
 import { name, version } from '../package.json';