Include licensing header into react.js

[solomatov]

Currently, react.js distribution has a licensing header. Unfortunately, it's removed by webpack and uglifyjs. Could you please add /*! at the file headers so that minifiers will keep them in optimized versions so that license compliance can be achieved in an automated manner,

[gaearon]

@solomatov Does #6539 help? If so, we can get it merged.

[solomatov]

@gaearon That will definitely help. Thank you!

[aweary]

@trueadm does the new build system handle this at all?

[trueadm]

@aweary I believe we do for development bundles, not for production bundles though. To save bytes.

https://github.com/facebook/react/blob/master/scripts/rollup/header.js

[gaearon]

Our headers look like this.

/** @license React v16.2.0
 * react-dom.production.min.js
 *
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

so that should be enough.