Clean up command help.

utils/pub/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 command_version;
 
 import 'pub.dart';
 
 /** Handles the `version` pub command. */
 class VersionCommand extends PubCommand {
-  String get description => 'print Pub version';
+  String get description => 'Print pub version.';
   String get usage => 'pub version';
   bool get requiresEntrypoint => false;
 
   Future onRun() {
     printVersion();
   }
 }