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 
format,
          bundleType,
          bundle.hasteName
        )
      )
    )
    .then(() => Packaging.createNodePackage(bundleType, packageName, filename))
    .then(() => {
      console.log(`${chalk.bgGreen.black(' COMPLETE ')} ${logKey}\n`);
    })
    .catch(error => {
      if (error.code) {
        console.error(`\x1b[31m-- ${error.code} (${error.plugin}) --`);
        console.error(error.message);
        console.error(error.loc);
        console.error(error.codeFrame);
      } else {
        console.error(error);
      }
      process.exit(1);
    });
}
rimraf('build', () => {
  
  fs.mkdirSync('build');
  
  fs.mkdirSync(join('build', 'packages'));
  
  fs.mkdirSync(join('build', 'dist'));
  const tasks = [