change host unavailable logic

Author: YangSen-qn

QiniuSDK/Http/QNResponseInfo.m

@@ -262,8 +262,7 @@ - (BOOL)canConnectToHost{
 
 - (BOOL)isHostUnavailable{
     // 基本不可恢复，注：会影响下次请求，范围太大可能会造成大量的timeout
-    if ((_statusCode >= -2000 && _statusCode <= -1200)
-        || _statusCode == 502 || _statusCode == 503 || _statusCode == 504 || _statusCode == 599) {
+    if (_statusCode == 502 || _statusCode == 503 || _statusCode == 504 || _statusCode == 599) {
         return true;
     } else {
         return false;