message: variables.get_global_step() is deprecated,  use `training_util.get_global_step()` instead
  error message:
  ```
  tensorflow/contrib/timeseries/python/timeseries/head.py:63: get_global_step (from tensorflow.contrib.framework.python.ops.variables) is deprecated and will be removed in a future version.
  ```
diff: @@ -19,7 +19,7 @@ from __future__ import print_function
  import re
  -from tensorflow.contrib.framework.python.ops import variables
  +from tensorflow.python.training import training_util
  from tensorflow.contrib.layers.python.layers import optimizers
  from tensorflow.contrib.timeseries.python.timeseries import feature_keys
  @@ -79,7 +79,7 @@ class _TimeSeriesRegressionHead(head_lib._Head): # pylint:disable=protected-acc
  train_op = optimizers.optimize_loss(
  model_outputs.loss,
  - global_step=variables.get_global_step(),
  + global_step=training_util.get_global_step(),
  optimizer=self.optimizer,
  # Learning rate is set in the Optimizer object
  learning_rate=None)
  