message: Fix comment in graph.go.
  Method name is AddGradients but not AddGradientsWithPrefix.
diff: @@ -147,7 +147,7 @@ func (g *Graph) Operations() []Operation {
  return ops
  }
  -// AddGradientsWithPrefix adds operations to compute the partial derivatives of sum of `y`s w.r.t `x`s,
  +// AddGradients adds operations to compute the partial derivatives of sum of `y`s w.r.t `x`s,
  // i.e., d(y_1 + y_2 + ...)/dx_1, d(y_1 + y_2 + ...)/dx_2...
  // This methods allows to caller to pass a custom name prefix to the operations
  // added to a graph to compute the gradients.
  