Fix on the bc_offline_training using deep copies

ml-agents/mlagents/trainers/bc/offline_trainer.py

 # Contains an implementation of Behavioral Cloning Algorithm
 
 import logging
+import copy
 
 from mlagents.trainers.bc.trainer import BCTrainer
 from mlagents.trainers.demo_loader import demo_to_buffer
             trainer_parameters['demo_path'],
             self.policy.sequence_length)
 
-        policy_brain = brain.__dict__
-        expert_brain = brain_params.__dict__
+        policy_brain = copy.deepcopy(brain.__dict__)
+        expert_brain = copy.deepcopy(brain_params.__dict__)
         policy_brain.pop('brain_name')
         expert_brain.pop('brain_name')
         if expert_brain != policy_brain: