fix(packages): use ES modules for primary build (#11120)

modules/@angular/router/src/router_config_loader.ts

@@ -14,7 +14,9 @@ import {of } from 'rxjs/observable/of';
 import {LoadChildren, Route} from './config';
 import {flatten, wrapIntoObservable} from './utils/collection';
 
-
+/**
+ * @experimental
+ */
 export const ROUTES = new OpaqueToken('ROUTES');
 
 export class LoadedRouterConfig {
@@ -44,4 +46,4 @@ export class RouterConfigLoader {
               t => offlineMode ? of (<any>t) : fromPromise(this.compiler.compileModuleAsync(t)));
     }
   }
-}
+}