Change Awake() to Start() in Spawning System (#120) (#136)

Issue #120

When the scenes are additively loaded, GameObject instantiation should be put in Start(), because Awake() is exectuted before the new scene becomes active.

Reference thread: https://forum.unity.com/threads/additive-scene-loading-and-awake.660379/

UOP1_Project/Assets/Scripts/SpawnSystem.cs

 	[SerializeField] private CameraManager _cameraManager;
 	[SerializeField] private Transform[] _spawnLocations;
 
-	void Awake()
+	void Start()
 	{
 		try
 		{