set TennisBrain's Brain Type to internal

unity-environment/Assets/ML-Agents/Examples/Tennis/Tennis.unity

     - 
     vectorActionSpaceType: 1
     vectorObservationSpaceType: 1
-  brainType: 2
+  brainType: 3
   CoreBrains:
   - {fileID: 635266522}
   - {fileID: 414188952}