message: Fix lack of `sess` attr in TensorBoard V1 callback.
  Fixes
diff: @@ -421,6 +421,7 @@ class TensorBoard(callbacks.Callback):
  embeddings_data = self.embeddings_data
  n_samples = embeddings_data[0].shape[0]
  i = 0
  + sess = K.get_session()
  while i < n_samples:
  step = min(self.batch_size, n_samples - i)
  batch = slice(i, i + step)
  @@ -438,8 +439,8 @@ class TensorBoard(callbacks.Callback):
  if not isinstance(K.learning_phase(), int):
  feed_dict[K.learning_phase()] = False
  - self.sess.run(self.assign_embeddings, feed_dict=feed_dict)
  - self.saver.save(self.sess,
  + sess.run(self.assign_embeddings, feed_dict=feed_dict)
  + self.saver.save(sess,
  os.path.join(self.log_dir, 'keras_embedding.ckpt'),
  epoch)
  