fix unity api warning

Author: psygames

Assets/UnityWebSocket/Scripts/Editor/SettingsWindow.cs

@@ -1,4 +1,4 @@
-using UnityEngine;
+using UnityEngine;
 using UnityEditor;
 using UnityEngine.Networking;
 using System.IO;
@@ -164,7 +164,7 @@ void BeginCheck()
 
         private void VersionCheckUpdate()
         {
-#if UNITY_2021_1_OR_NEWER
+#if UNITY_2020_3_OR_NEWER
             if (req == null
                 || req.result == UnityWebRequest.Result.ConnectionError
                 || req.result == UnityWebRequest.Result.DataProcessingError