message: Make gradient docstring consistent
diff: @@ -940,7 +940,8 @@ class GradientTape(object):
  """Computes the gradient using operations recorded in context of this tape.
  Args:
  - target: Tensor (or list of tensors) to be differentiated.
  + target: a list or nested structure of Tensors or Variables to be
  + differentiated.
  sources: a list or nested structure of Tensors or Variables. `target`
  will be differentiated against elements in `sources`.
  output_gradients: a list of gradients, one for each element of
  