Pyarrow version error
Hi @Zaker237, thanks for reporting.

This is weird: the error you get is only thrown if the installed pyarrow version is less than 3.0.0.

Could you please check that you install pyarrow in the same Python virtual environment where you installed datasets?

From the Python command line (or terminal) where you get the error, please type:
```
import pyarrow
print(pyarrow.__version__)
import datasets
print(datasets.__version__)
```  hi @albertvillanova  i try yesterday to create a new python environement with python 7 and try it on the environement and it worked. so i think that the error was not the package but may be jupyter notebook on conda. still yet i'm not yet sure but it worked in an environment created with venv OK, thanks @Zaker237 for your feedback.

I close this issue then. Please, feel free to reopen it if the problem arises again.
## Describe the bug
I installed datasets(version 1.17.0, 1.18.0, 1.18.3) but i'm right now nor able to import it because of pyarrow. when i try to import it, i get the following error:
`To use datasets, the module pyarrow>=3.0.0 is required, and the current version of pyarrow doesn't match this condition`.
i tryed with all version of pyarrow execpt `4.0.0` but still get the same error.

## Steps to reproduce the bug
```python
import datasets
```

## Expected results
A clear and concise description of the expected results.

## Actual results
AttributeError                            Traceback (most recent call last)
<ipython-input-19-652e886d387f> in <module>
----> 1 import datasets

~\AppData\Local\Continuum\anaconda3\lib\site-packages\datasets\__init__.py in <module>
     26 
     27 
---> 28 if _version.parse(pyarrow.__version__).major < 3:
     29     raise ImportWarning(
     30         "To use `datasets`, the module `pyarrow>=3.0.0` is required, and the current version of `pyarrow` doesn't match this condition.\n"

AttributeError: 'Version' object has no attribute 'major'

## Environment info
Traceback (most recent call last):
  File "c:\users\alex\appdata\local\continuum\anaconda3\lib\runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "c:\users\alex\appdata\local\continuum\anaconda3\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\Users\Alex\AppData\Local\Continuum\anaconda3\Scripts\datasets-cli.exe\__main__.py", line 5, in <module>
  File "c:\users\alex\appdata\local\continuum\anaconda3\lib\site-packages\datasets\__init__.py", line 28, in <module>
    if _version.parse(pyarrow.__version__).major < 3:
AttributeError: 'Version' object has no attribute 'major'

- `datasets` version:
- Platform: Linux(Ubuntu) and Windows: conda on the both
- Python version: 3.7
- PyArrow version: 7.0.0
