tokenizer.vocab key and values is change begin line 261?
transformers version 3.0.0

```python
tokenizer = BertTokenizer.from_pretrained('bert-base-chinese')

for v, i in tokenizer.vocab.items():
    print(v, i)
```

![image](https://user-images.githubusercontent.com/18568380/97958832-04cc1080-1de9-11eb-8c2b-0463c902853e.png)
i find key and values maybe wrong position.
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