[Unity3D-sdk] Fix isVRSupported error in Unity 5

This commit fixes the compile errors:
- Unity 5.0: ```Assets/PocoSDK/VRSupport.cs(42,44): error CS0234: The type or namespace name `VR' does not exist in the namespace `UnityEngine'. Are you missing an assembly reference?```
- Unity 5.1-5.3: ```Assets/PocoSDK/VRSupport.cs(42,58): error CS0117: `UnityEngine.VR.VRSettings' does not contain a definition for `loadedDeviceName'```

Property UnityEngine.VR.VRSettings.loadedDeviceName was released in Unity 5.4: https://docs.unity3d.com/540/Documentation/ScriptReference/VR.VRSettings-loadedDeviceName.html

Unity3D/VRSupport.cs

@@ -36,10 +36,10 @@ public void PeekCommand()
 
     public object isVRSupported(List<object> param)
     {
-#if UNITY_3 || UNITY_4
-			return false;
-#elif UNITY_5 || UNITY_2017_1
-			return UnityEngine.VR.VRSettings.loadedDeviceName.Equals("CARDBOARD");
+#if !UNITY_5_4_OR_NEWER
+		return false;
+#elif !UNITY_2017_2_OR_NEWER
+		return UnityEngine.VR.VRSettings.loadedDeviceName.Equals("CARDBOARD");
 #else
         return UnityEngine.XR.XRSettings.loadedDeviceName.Equals("CARDBOARD");
 #endif