documentation: fix underline

Author: bonellia

doc/frameworks/tensorflow/deploying_tensorflow_serving.rst

@@ -273,7 +273,7 @@ refer to TensorFlow's `Save and Restore <https://www.tensorflow.org/guide/saved_
 inference-time behavior of your SavedModels.
 
 Providing Python scripts for pre/post-processing
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 You can add your customized Python code to process your input and output data.
 This customized Python code must be named ``inference.py`` and specified through the ``entry_point`` parameter: