Bump DEPS to grab linter `0.1.20`.
Bump DEPS to grab linter `0.1.20`.

* Fixes `iterable_contains_unrelated_type `.
* Adds `cancel_subscriptions` lint.
* Adds`close_sinks` lint.

BUG=
R=scheglov@google.com

Review URL: https://codereview.chromium.org/2061913003 .

dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk