fix: error in C#

csharp/core/Common.cs

@@ -24,13 +24,14 @@ namespace AlibabaCloud.TeaUtil
     public static class Common
     {
         private static readonly string _defaultUserAgent;
-        private static readonly _processStartTime;
+        private static readonly long _processStartTime;
         private static long _seqId = 0;
 
         static Common()
         {
             _defaultUserAgent = GetDefaultUserAgent();
-            _processStartTime = Process.GetCurrentProcess().StartTime;
+            double ticks = (DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalSeconds;
+            _processStartTime = (long)(ticks * 1000);
         }
 
         public static byte[] ToBytes(string val)
@@ -136,7 +137,7 @@ public static string GetNonce()
             long currentTime = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
             long seq = Interlocked.Increment(ref seqId);
             long randNum = new Random().NextInt64();
-            string msg = $"{process_start_time}-{thread_id}-{current_time}-{seq}-{randNum}";
+            string msg = string.Format("{0}-{1}-{2}-{3}", _processStartTime, threadId, currentTime, seq, randNum);
             using (MD5 md5 = MD5.Create())
             {
                 byte[] hash = md5.ComputeHash(System.Text.Encoding.UTF8.GetBytes(msg));