Fix(@schematics/angular): correspond Fetch as Google

Fetch as Google (Google's bot checker) use ES5. So ES5 require polyfills (`Fetch as Google` need `core-js/es6/array` only ).
I think that Angular needs a response to Google in order to become a PWA. 

thanks.

Author: rdlabo

packages/schematics/angular/application/files/src/polyfills.ts

@@ -28,7 +28,7 @@
 // import 'core-js/es6/math';
 // import 'core-js/es6/string';
 // import 'core-js/es6/date';
-// import 'core-js/es6/array';
+import 'core-js/es6/array';
 // import 'core-js/es6/regexp';
 // import 'core-js/es6/map';
 // import 'core-js/es6/weak-map';