Update API to version 5 (#1179)

UnitySDK/Assets/ML-Agents/Scripts/Academy.cs

              "docs/Learning-Environment-Design-Academy.md")]
     public abstract class Academy : MonoBehaviour
     {
-        private const string kApiVersion = "API-4";
+        private const string kApiVersion = "API-5";
 
         // Fields provided in the Inspector
 

ml-agents/mlagents/envs/environment.py

         atexit.register(self._close)
         self.port = base_port + worker_id
         self._buffer_size = 12000
-        self._version_ = "API-4"
+        self._version_ = "API-5"
         self._loaded = False    # If true, this means the environment was successfully loaded
         self.proc1 = None       # The process that is started. If None, no process was started
         self.communicator = self.get_communicator(worker_id, base_port)

ml-agents/tests/mock_communicator.py

         )
         rl_init = UnityRLInitializationOutput(
             name="RealFakeAcademy",
-            version="API-4",
+            version="API-5",
             log_path="",
             brain_parameters=[bp]
         )

ml-agents/tests/trainers/test_trainer_controller.py

               "brainNames": ["RealFakeBrain"],
               "externalBrainNames": ["RealFakeBrain"],
               "logPath":"RealFakePath",
-              "apiNumber":"API-3",
+              "apiNumber":"API-5",
               "brainParameters": [{
                   "vectorObservationSize": 3,
                   "numStackedVectorObservations" : 2,