vince's fix for model step (#1329)

ml-agents/mlagents/trainers/trainer.py

         """
         raise UnityTrainerException("The update_model method was not implemented.")
 
-    def save_model(self, steps):
+    def save_model(self):
-        :param steps: The number of steps of training
-        self.policy.save_model(steps)
+        self.policy.save_model(self.get_step)
 
     def export_model(self):
         """

ml-agents/mlagents/trainers/trainer_controller.py

         :param saver: Tensorflow saver for session.
         """
         for brain_name in self.trainers.keys():
-            self.trainers[brain_name].save_model(steps)
+            self.trainers[brain_name].save_model()
         self.logger.info('Saved Model')
 
     def _export_graph(self):