ALBERT pretrained tokenizer loading failed on Google Colab
Author: PeterQiu0516
Pull request: no

I tried the example code for ALBERT model on Google Colab:

```
from transformers import AlbertTokenizer, AlbertModel
import torch
tokenizer = AlbertTokenizer.from_pretrained('albert-base-v2')
model = AlbertModel.from_pretrained('albert-base-v2')
inputs = tokenizer("Hello, my dog is cute", return_tensors="pt")
outputs = model(**inputs)
last_hidden_states = outputs.last_hidden_state
```

![image](https://user-images.githubusercontent.com/47267715/113908950-228d0f80-97a5-11eb-8f5d-0f14487770a0.png)


Error Message:
```
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-23-b4da0546b72a> in <module>()
      5 model = AlbertModel.from_pretrained('albert-base-v2')
      6 
----> 7 inputs = tokenizer("Hello, my dog is cute", return_tensors="pt")
      8 outputs = model(**inputs)
      9 last_hidden_states = outputs.last_hidden_state

TypeError: 'NoneType' object is not callable
```
It seems that the ALBERT tokenizer failed to load correctly. And I tried BERT's pretrained tokenizer and it could be loaded correctly instead.

BERT tokenizer:
![image](https://user-images.githubusercontent.com/47267715/113909416-a6df9280-97a5-11eb-9b4f-6f5f9cd416d0.png)




Comments:
Have you installed the [sentencepiece](https://github.com/google/sentencepiece) library?

> Have you installed the [sentencepiece](https://github.com/google/sentencepiece) library?

Yes.

```
!pip install transformers
!pip install sentencepiece
```

```
Requirement already satisfied: transformers in /usr/local/lib/python3.7/dist-packages (4.5.0)
Requirement already satisfied: numpy>=1.17 in /usr/local/lib/python3.7/dist-packages (from transformers) (1.19.5)
Requirement already satisfied: tqdm>=4.27 in /usr/local/lib/python3.7/dist-packages (from transformers) (4.41.1)
Requirement already satisfied: requests in /usr/local/lib/python3.7/dist-packages (from transformers) (2.23.0)
Requirement already satisfied: importlib-metadata; python_version < "3.8" in /usr/local/lib/python3.7/dist-packages (from transformers) (3.8.1)
Requirement already satisfied: filelock in /usr/local/lib/python3.7/dist-packages (from transformers) (3.0.12)
Requirement already satisfied: sacremoses in /usr/local/lib/python3.7/dist-packages (from transformers) (0.0.44)
Requirement already satisfied: tokenizers<0.11,>=0.10.1 in /usr/local/lib/python3.7/dist-packages (from transformers) (0.10.2)
Requirement already satisfied: regex!=2019.12.17 in /usr/local/lib/python3.7/dist-packages (from transformers) (2019.12.20)
Requirement already satisfied: packaging in /usr/local/lib/python3.7/dist-packages (from transformers) (20.9)
Requirement already satisfied: chardet<4,>=3.0.2 in /usr/local/lib/python3.7/dist-packages (from requests->transformers) (3.0.4)
Requirement already satisfied: certifi>=2017.4.17 in /usr/local/lib/python3.7/dist-packages (from requests->transformers) (2020.12.5)
Requirement already satisfied: urllib3!=1.25.0,!=1.25.1,<1.26,>=1.21.1 in /usr/local/lib/python3.7/dist-packages (from requests->transformers) (1.24.3)
Requirement already satisfied: idna<3,>=2.5 in /usr/local/lib/python3.7/dist-packages (from requests->transformers) (2.10)
Requirement already satisfied: zipp>=0.5 in /usr/local/lib/python3.7/dist-packages (from importlib-metadata; python_version < "3.8"->transformers) (3.4.1)
Requirement already satisfied: typing-extensions>=3.6.4; python_version < "3.8" in /usr/local/lib/python3.7/dist-packages (from importlib-metadata; python_version < "3.8"->transformers) (3.7.4.3)
Requirement already satisfied: six in /usr/local/lib/python3.7/dist-packages (from sacremoses->transformers) (1.15.0)
Requirement already satisfied: joblib in /usr/local/lib/python3.7/dist-packages (from sacremoses->transformers) (1.0.1)
Requirement already satisfied: click in /usr/local/lib/python3.7/dist-packages (from sacremoses->transformers) (7.1.2)
Requirement already satisfied: pyparsing>=2.0.2 in /usr/local/lib/python3.7/dist-packages (from packaging->transformers) (2.4.7)
Requirement already satisfied: sentencepiece in /usr/local/lib/python3.7/dist-packages (0.1.95)
```

I restart the runtime and it is fixed now. Seems like some strange compatibility issues with colab.