Fix dart_style version.

DEPS

 # 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.
 
 vars = {
   # The dart_root is the root of our sdk checkout. This is normally
   # simply sdk, but if using special gclient specs it can be different.
   "dart_root": "sdk",
 
   # We use mirrors of all github repos to guarantee reproducibility and
@@ skipping 38 matching lines @@
   "charcode_tag": "@1.1.0",
   "chrome_rev" : "@19997",
   "cli_util_tag" : "@0.0.1+3",
   "code_transformers_tag": "@v0.4.2+3",
   "collection_tag": "@1.9.1",
   "convert_tag": "@2.0.1",
   "crypto_tag" : "@2.0.1",
   "csslib_tag" : "@0.13.2",
   "dart2js_info_tag" : "@0.5.0",
   "dart_services_rev" : "@7aea2574e6f3924bf409a80afb8ad52aa2be4f97",
-  "dart_style_tag": "@0.2.11+1",
+  "dart_style_tag": "@v0.2.11+1",
   "dartdoc_tag" : "@v0.9.7+6",
   "fixnum_tag": "@0.10.5",
   "func_tag": "@0.1.0",
   "glob_tag": "@1.1.3",
   "html_tag" : "@0.13.0",
   "http_multi_server_tag" : "@2.0.2",
   "http_parser_tag" : "@3.0.2",
   "http_tag" : "@0.11.3+9",
   "http_throttle_rev" : "@284344cd357e435c6c8ff9a4a21f02b9e384a541",
   "idl_parser_rev": "@7fbe68cab90c38147dee4f48c30ad0d496c17915",
@@ skipping 495 matching lines @@
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',
     'pattern': '.',
     'action': ['python', 'sdk/build/vs_toolchain.py', 'update'],
   },
   {
     "pattern": ".",
     "action": ["python", Var("dart_root") + "/tools/generate_buildfiles.py"],
   },
 ]