attr error while installing with pip, pip installation shouldn’t be 'sudo' prefixed
error while installing with pip3
```
silkaj
Traceback (most recent call last):
File "/home/thomas/.local/bin/silkaj", line 20, in <module>
from silkaj.cli_tools import cli
File "/home/thomas/.local/lib/python3.7/site-packages/silkaj/cli_tools.py", line 22, in <module>
from silkaj.tx import send_transaction
File "/home/thomas/.local/lib/python3.7/site-packages/silkaj/tx.py", line 24, in <module>
from silkaj.network_tools import ClientInstance, HeadBlock
File "/home/thomas/.local/lib/python3.7/site-packages/silkaj/network_tools.py", line 25, in <module>
from duniterpy.api.client import Client
File "/home/thomas/.local/lib/python3.7/site-packages/duniterpy/api/client.py", line 9, in <module>
import jsonschema
File "/home/thomas/.local/lib/python3.7/site-packages/jsonschema/__init__.py", line 12, in <module>
from jsonschema.exceptions import (
File "/home/thomas/.local/lib/python3.7/site-packages/jsonschema/exceptions.py", line 141, in <module>
@attr.s(hash=True)
AttributeError: module 'attr' has no attribute 's'
```
issue