Fix wrong fairseq version in setup.py

[SuJiaKuan]

When I install LAMA via pip (command: pip install --editable .) and run the sentence filling script (lama/eval_generation.py), the following error occurs:

Traceback (most recent call last):
  File "lama/eval_generation.py", line 7, in <module>
    from lama.modules import build_model_by_name
  File "/home/feabries/projects/LAMA/lama/modules/__init__.py", line 11, in <module>
    from .roberta_connector import Roberta
  File "/home/feabries/projects/LAMA/lama/modules/roberta_connector.py", line 7, in <module>
    from fairseq.models.roberta import RobertaModel
ModuleNotFoundError: No module named 'fairseq.models.roberta'

The error comes from the line in lama/modules/roberta_connector.py, which imports Roberta model class using fairseq:

LAMA/lama/modules/roberta_connector.py

Line 7 in 5cba81b

from fairseq.models.roberta import RobertaModel

It seems that the versions of fairseq in requirements.txt and setup.py are different (#42). The above code works fine for fairseq==0.8.0, but fails on fairseq==0.6.1, so I change the fairseq version to 0.8.0 in setup.py in the pull request.