message: Update old docstring references to point to the new location
  `tf.distribute.Strategy`.
diff: @@ -85,9 +85,9 @@ class VariableSynchronization(enum.Enum):
  class VariableAggregationV2(enum.Enum):
  """Indicates how a distributed variable will be aggregated.
  - `tf.contrib.distribute.DistributionStrategy` distributes a model by making
  - multiple copies (called "replicas") acting data-parallel on different elements
  - of the input batch. When performing some variable-update operation, say
  + `tf.distribute.Strategy` distributes a model by making multiple copies
  + (called "replicas") acting data-parallel on different elements of the input
  + batch. When performing some variable-update operation, say
  `var.assign_add(x)`, in a model, we need to resolve how to combine the
  different values for `x` computed in the different replicas.
  