message: Fix warnings in tf.contrib.bayesflow.monte_carlo.expectation
  This fix fixes several warnings in tf.contrib.bayesflow.monte_carlo.expectation
  by switching to keepdims for tf.reduce_mean.
diff: @@ -328,7 +328,7 @@ def expectation(f, samples, log_prob=None, use_reparametrization=True,
  if not callable(f):
  raise ValueError('`f` must be a callable function.')
  if use_reparametrization:
  - return math_ops.reduce_mean(f(samples), axis=axis, keep_dims=keep_dims)
  + return math_ops.reduce_mean(f(samples), axis=axis, keepdims=keep_dims)
  else:
  if not callable(log_prob):
  raise ValueError('`log_prob` must be a callable function.')
  @@ -348,7 +348,7 @@ def expectation(f, samples, log_prob=None, use_reparametrization=True,
  # "Is there a floating point value of x, for which x-x == 0 is false?"
  # http://stackoverflow.com/q/2686644
  fx += stop(fx) * (logpx - stop(logpx)) # Add zeros_like(logpx).
  - return math_ops.reduce_mean(fx, axis=axis, keep_dims=keep_dims)
  + return math_ops.reduce_mean(fx, axis=axis, keepdims=keep_dims)
  def _sample_mean(values):
  