Fix missing action axis in Tennis (#3732)

* Fix missing action axis in Tennis

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

Fix typo

Co-Authored-By: Chris Elion <chris.elion@unity3d.com>

Co-authored-by: Chris Elion <chris.elion@unity3d.com>

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

 
     public override float[] Heuristic()
     {
-        var action = new float[2];
+        var action = new float[3];
-        action[0] = Input.GetAxis("Horizontal");
-        action[1] = Input.GetKey(KeyCode.Space) ? 1f : 0f;
+        action[0] = Input.GetAxis("Horizontal");    // Racket Movement
+        action[1] = Input.GetKey(KeyCode.Space) ? 1f : 0f;   // Racket Jumping
+        action[2] = Input.GetAxis("Vertical");   // Racket Rotation  
         return action;
     }