Guard polyfills against window possibly being undefined

packages/react-app-polyfill/ie11.js

@@ -11,7 +11,7 @@ if (typeof Promise === 'undefined') {
  // inconsistent state due to an error, but it gets swallowed by a Promise,
  // and the user has no idea what causes React's erratic future behavior.
  require('promise/lib/rejection-tracking').enable();
- window.Promise = require('promise/lib/es6-extensions.js');
+ self.Promise = require('promise/lib/es6-extensions.js');
 }
 
 // Make sure we're in a Browser-like environment before importing polyfills

packages/react-app-polyfill/ie9.js

@@ -11,4 +11,5 @@ require('./ie11');
 // React 16+ relies on Map, Set, and requestAnimationFrame
 require('core-js/features/map');
 require('core-js/features/set');
-require('raf').polyfill(window);
+
+require('raf').polyfill();