added timepenalty to obs

Project/Assets/ML-Agents/Examples/Tennis/Prefabs/TennisArea.prefab

   m_Name: 
   m_EditorClassIdentifier: 
   m_BrainParameters:
-    vectorObservationSize: 10
+    vectorObservationSize: 11
     numStackedVectorObservations: 3
     vectorActionSize: 03000000
     vectorActionDescriptions: []
   m_Name: 
   m_EditorClassIdentifier: 
   m_BrainParameters:
-    vectorObservationSize: 10
+    vectorObservationSize: 11
     numStackedVectorObservations: 3
     vectorActionSize: 03000000
     vectorActionDescriptions: []

Project/Assets/ML-Agents/Examples/Tennis/Scripts/TennisAgent.cs

         sensor.AddObservation(m_InvertMult * gameObject.transform.rotation.z);
         
         sensor.AddObservation(System.Convert.ToInt32(m_BallScript.lastFloorHit == HitWall.FloorHit.FloorHitUnset));
+        sensor.AddObservation(-1 * timePenalty);
     }
 
     public override void OnActionReceived(float[] vectorAction)