Fix: add 'import tensorflow as tf' required by _save_tf_model (#1560)

Co-authored-by: Felipe Antunes <[email protected]>

Author: felipeeeantunes

reinforcement_learning/common/sagemaker_rl/coach_launcher.py

@@ -8,6 +8,7 @@
 import rl_coach.core_types 
 from rl_coach import logger
 from rl_coach.logger import screen
+import tensorflow as tf
 import argparse
 import copy
 import logging