Our built files are missing license headers. 

cjs has no headers:
https://unpkg.com/react@16.0.0-beta.5/cjs/react.development.js
https://unpkg.com/react-dom@16.0.0-beta.5/cjs/react-dom.development.js

umd has headers identifying the bundle name but not the license:
https://unpkg.com/react@16.0.0-beta.5/umd/react.development.js
https://unpkg.com/react-dom@16.0.0-beta.5/umd/react-dom.development.js

Both should have license headers similar to this:

```
/**
 * React v15.6.1
 *
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 */
```

We likely just need to change the code in getBanner in scripts/rollup/build.js. https://github.com/facebook/react/blob/b4a3e3b34594759c90aef1694d2166b2d1126fa1/scripts/rollup/build.js#L78

You can test by running `yarn build` and looking in build/packages.

cc @trueadm 
Packaging.createFacebookWWWBuild,
    Packaging.createReactNativeBuild,
  ];
  for (const bundle of Bundles.bundles) {
    tasks.push(
      () => createBundle(bundle, UMD_DEV),
      () => createBundle(bundle, UMD_PROD),
      () => createBundle(bundle, NODE_DEV),
      () => createBundle(bundle, NODE_PROD),
      () => createBundle(bundle, FB_DEV),
      () => createBundle(bundle, FB_PROD),
      () => createBundle(bundle, RN_DEV),
      () => createBundle(bundle, RN_PROD)
    );
  }
  if (syncFbsource) {
    tasks.push(() =>
      syncReactNative(join('build', 'react-native'), syncFbsource)
    );
  } else if (syncWww) {
    tasks.push(() => syncReactDom(join('build', 'facebook-www'), syncWww));
  }
  
  
  
  return runWaterfall(tasks)
    .then(() => {
      
      console.log(Stats.printResults());