fix bug

fix:using utf8 encoding get strings instead of default coding

Author: boxiaowpl

sdk/Aliyun/OTS/ProtoBuffer/SearchVariantType.cs

@@ -75,15 +75,15 @@ public static byte[] FromString(string v)
         {
             using (MemoryStream ms = new MemoryStream())
             {
-                byte[] strBytes = UTF8Encoding.Default.GetBytes(v);
+                byte[] strBytes = Encoding.UTF8.GetBytes(v);
 
                 ms.WriteByte(VT_STRING);
                 foreach (var item in BitConverter.GetBytes(strBytes.Length))
                 {
                     ms.WriteByte(item);
                 }
 
-                foreach (var item in UTF8Encoding.Default.GetBytes(v))
+                foreach (var item in Encoding.UTF8.GetBytes(v))
                 {
                     ms.WriteByte(item);
                 }