small per timestep reward

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

     {
         if (c.gameObject.CompareTag("ball"))
         {
-            AddReward(.2f * m_BallTouch);
+            AddReward(.02f + .18f * m_BallTouch);
         }
     }
     public override void OnEpisodeBegin()