- Fix outdated use of factory clause.

bin/platform.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * The [Platform] class exposes details of the machine and operating
  * system.
  */
-interface Platform factory _Platform {
+interface Platform default _Platform {
   /**
    * Create a Platform object.
    */
   Platform();
 
   /**
    * Get the number of processors of the machine.
    */
   int numberOfProcessors();
 
   /**
    * Get the path separator used by the operating system to separate
    * components in file paths.
    */
   String pathSeparator();
 
   /**
    * Get a string ('macos', 'windows', 'linux') representing the
    * operating system.
    */
   String operatingSystem();
 }