Update ml-agents/mlagents/trainers/policy/tf_policy.py

Co-authored-by: Vincent-Pierre BERGES <vincentpierre@unity3d.com>

ml-agents/mlagents/trainers/policy/tf_policy.py

         )
         if self.action_spec.continuous_size > 0 and self.action_spec.discrete_size > 0:
             raise UnityPolicyException(
-                "Tensorflow does not support mixed action spaces. Please run with --torch."
+                "TensorFlow does not support mixed action spaces. Please run with the Torch framework."
             )
         # for ghost trainer save/load snapshots
         self.assign_phs: List[tf.Tensor] = []