fix:去掉不参与签名字段

@@ -65,7 +65,7 @@ class Signature
         $this->sortByASCII();
 
         $string = $this->map($this->item, function ($k, $v) {
-            return !($v === '' || $v === null);
+            return !($v === '' || $v === null || $k === 'service');
         });
 
         return self::encode($string);