message: fix kokoro build :deprecated message.
diff: @@ -736,7 +736,7 @@ class _DictWrapper(TrackableDataStructure, wrapt.ObjectProxy):
  if wrapped_dict is None:
  # Allow zero-argument construction, e.g. from session.run's re-wrapping.
  wrapped_dict = {}
  - if not isinstance(wrapped_dict, collections.Mapping):
  + if not isinstance(wrapped_dict, collections_abc.Mapping):
  # Allow construction from a sequence, e.g. from nest.pack_sequence_as.
  wrapped_dict = dict(wrapped_dict)
  wrapt.ObjectProxy.__init__(self, wrapped_dict)
  