Dart: Change url of Dart repository in gclient recipe module Dart config.
Dart: Change url of Dart repository in gclient recipe module Dart config.

Bug:
Change-Id: I031f5787a87a4bddbd3492912814476daf2c9b4f
Reviewed-on: https://chromium-review.googlesource.com/738118
Commit-Queue: William Hesse <a821cddceae7dc400f272e3cb1a72f400f9fed6d@google.com>
Reviewed-by: Paweł Hajdan Jr. <84cab74a96a175cf90ed68b8abab420352923e11@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools