Update pub to use the new command runner API in args.

sdk/lib/_internal/pub/lib/src/command/version.dart

 // Copyright (c) 2012, 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.
 
 library pub.command.version;
 
-import 'dart:async';
-
 import '../command.dart';
 import '../log.dart' as log;
 import '../sdk.dart' as sdk;
 
 /// Handles the `version` pub command.
 class VersionCommand extends PubCommand {
+  String get name => "version";
   String get description => "Print pub version.";
-  String get usage => "pub version";
+  String get invocation => "pub version";
 
-  Future onRun() {
+  void run() {
     log.message("Pub ${sdk.version}");
-    return null;
   }
 }