Update dartdoc to 0.13.0+2.

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.
 
 # IMPORTANT:
 # Before adding or updating dependencies, please review the documentation here:
 # https://github.com/dart-lang/sdk/wiki/Adding-and-Updating-Dependencies
 
 vars = {
   # The dart_root is the root of our sdk checkout. This is normally
@@ skipping 59 matching lines @@
   # Please follow this process to make updates:
   #   * file an issue with area-infrastructure requesting a roll for this
   #     package (please also indicate what version to roll).
   #   * let the infrastructure team submit the change on your behalf,
   #     so they can build a new dev release and roll the submitted sdks a few
   #     minutes later.
   #
   # For more details, see https://github.com/dart-lang/sdk/issues/30164
   "dart_style_tag": "@1.0.7",  # Please see the note above before updating.
 
-  "dartdoc_tag" : "@v0.13.0+1",
+  "dartdoc_tag" : "@v0.13.0+2",
   "fixnum_tag": "@0.10.5",
   "func_tag": "@1.0.0",
   "glob_tag": "@1.1.3",
   "html_tag" : "@0.13.1",
   "http_multi_server_tag" : "@2.0.3",
   "http_parser_tag" : "@3.1.1",
   "http_tag" : "@0.11.3+14",
   "http_throttle_tag" : "@1.0.1",
   "idl_parser_rev": "@7fbe68cab90c38147dee4f48c30ad0d496c17915",
   "intl_tag": "@0.14.0",
@@ skipping 388 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"],
   },
 ]