Update license for the gr-diff-builder-element.js file

The file must contain "@license" in the license text.

Change-Id: Ic65610d223079d601bd99d656290500140294c00

polygerrit-ui/app/elements/diff/gr-diff-builder/gr-diff-builder-element.js

@@ -1,16 +1,19 @@
-// Copyright (C) 2020 The Android Open Source Project
+/**
-//
+ * @license
-// Licensed under the Apache License, Version 2.0 (the "License");
+ * Copyright (C) 2020 The Android Open Source Project
-// you may not use this file except in compliance with the License.
+ *
-// You may obtain a copy of the License at
+ * Licensed under the Apache License, Version 2.0 (the 'License');
-//
+ * you may not use this file except in compliance with the License.
-// http://www.apache.org/licenses/LICENSE-2.0
+ * You may obtain a copy of the License at
-//
+ *
-// Unless required by applicable law or agreed to in writing, software
+ * http://www.apache.org/licenses/LICENSE-2.0
-// distributed under the License is distributed on an "AS IS" BASIS,
+ *
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * Unless required by applicable law or agreed to in writing, software
-// See the License for the specific language governing permissions and
+ * distributed under the License is distributed on an 'AS IS' BASIS,
-// limitations under the License.
+ * 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.
+ */
 (function() {
   'use strict';