Update dartdoc to v0.13.0+1.

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 48 matching lines @@
   "chrome_rev" : "@19997",
   "cli_util_tag" : "@0.1.0",
   "code_transformers_tag": "@v0.5.1",
   "collection_tag": "@1.13.0",
   "convert_tag": "@2.0.1",
   "crypto_tag" : "@2.0.1",
   "csslib_tag" : "@0.13.3+1",
   "dart2js_info_tag" : "@0.5.4+2",
   "dart_services_rev" : "@7aea2574e6f3924bf409a80afb8ad52aa2be4f97",
   "dart_style_tag": "@1.0.6",
-  "dartdoc_tag" : "@v0.12.0",
+  "dartdoc_tag" : "@v0.13.0+1",
   "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+9",
   "http_throttle_tag" : "@1.0.1",
   "idl_parser_rev": "@7fbe68cab90c38147dee4f48c30ad0d496c17915",
   "initialize_tag": "@v0.6.2+5",
   "intl_tag": "@0.14.0",
   "isolate_tag": "@1.0.0",
   "jinja2_rev": "@2222b31554f03e62600cd7e383376a7c187967a1",
   "json_rpc_2_tag": "@2.0.4",
   "linter_tag": "@0.1.31",
   "logging_tag": "@0.11.3+1",
-  "markdown_tag": "@0.11.2",
+  "markdown_tag": "@0.11.3",
   "matcher_tag": "@0.12.0+2",
   "metatest_tag": "@0.2.2+3",
   "mime_rev": "@75890811d4af5af080351ba8a2853ad4c8df98dd",
   "mustache4dart_tag" : "@v1.1.0",
   "oauth2_tag": "@1.0.2",
   "observable_tag": "@0.17.0",
   "observatory_pub_packages_rev": "@26aad88f1c1915d39bbcbff3cad589e2402fdcf1",
   "observe_tag": "@0.15.0",
   "package_config_tag": "@1.0.0",
   "package_resolver_tag": "@1.0.2+1",
@@ skipping 393 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"],
   },
 ]