在调用auto_setup()时传入logdir后，调用assert_not_equal(None, UIProxyObj, "blabla")会报循环引用错误

### 重现步骤：
1.引入相关包
```
from airtest.core.api import *
from poco.drivers.std import StdPoco
```

2.装载测试环境
```
auto_setup(__file__, logdir="/Users/blablabla/airtestLog")
```

3.实例化poco
```
poco = StdPoco()
```

4.让poco自然返回一个proxy对象
```
a = poco(name="treasureBtn")
```

5.调用assert_not_equal()
```
assert_not_equal(None, a, "324234324")
```

--------------------------------------------------------------
### 结果：
报循环引用错误
```
Traceback (most recent call last):
File "", line 1, in
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/airtest/utils/logwraper.py", line 86, in wrapper
logger.log('function', fndata)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/airtest/utils/logwraper.py", line 57, in log
log_data = json.dumps({'tag': tag, 'depth': depth, 'time': time.time(), 'data': data}, default=self._dumper)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/__init__.py", line 238, in dumps
**kw).encode(obj)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 199, in encode
chunks = self.iterencode(o, _one_shot=True)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 257, in iterencode
return _iterencode(o, 0)
ValueError: Circular reference detected
```

--------------------------------------------------------------
### 环境：
```
编码环境：python控制台
设备：vivo x21a
游戏引擎：cocos2d-lua
操作系统：macOS 10.15.6
airtest.core.api版本：1.1.3
python版本：3.6.5
```