Colab Notebook breaks when downloading the squad dataset
The notebook forces version 0.1.0. If I use the latest, things work, I'll run the whole notebook and create a PR.

But in the meantime, this issue gets fixed by changing:
`!pip install nlp==0.1.0`
to
`!pip install nlp` It still breaks very near the end

![image](https://user-images.githubusercontent.com/338917/83312264-aa96a600-a1df-11ea-987f-2f4a0474247e.png)
 When you install `nlp` for the first time on a Colab runtime, it updates the `pyarrow` library that was already on colab. This update shows this message on colab:
```
WARNING: The following packages were previously imported in this runtime:
  [pyarrow]
You must restart the runtime in order to use newly installed versions.
```
You just have to restart the runtime and it should be fine.
If you don't restart, then it breaks like in your first message  Thanks for reporting the second one ! We'll update the notebook to fix this one :) This trick from @thomwolf seems to be the most reliable solution to fix this colab notebook issue:

```python
# install nlp
!pip install -qq nlp==0.2.0

# Make sure that we have a recent version of pyarrow in the session before we continue - otherwise reboot Colab to activate it
import pyarrow
if int(pyarrow.__version__.split('.')[1]) < 16:
    import os
    os.kill(os.getpid(), 9)
``` The second part got fixed here: 2cbc656d6fc4b18ce57eac070baec05b31180d39

Thanks! I'm then closing this issue.
When I run the notebook in Colab
https://colab.research.google.com/github/huggingface/nlp/blob/master/notebooks/Overview.ipynb
breaks when running this cell:
![image](https://user-images.githubusercontent.com/338917/83311709-ffd1b800-a1dd-11ea-8394-3a87df0d7f8b.png)
