message: Update the state_size of LSTM cell to be list, instead of a tuple.
  This will make the type of states in the step_function to be consistent with
  the state_size.
diff: @@ -2030,7 +2030,7 @@ class LSTMCell(Layer):
  self.dropout = min(1., max(0., dropout))
  self.recurrent_dropout = min(1., max(0., recurrent_dropout))
  self.implementation = implementation
  - self.state_size = (self.units, self.units)
  + self.state_size = [self.units, self.units]
  self.output_size = self.units
  self._dropout_mask = None
  self._recurrent_dropout_mask = None
  