make test_bert_tokenizer use absolute path

import pytest

import os

from os.path import join

@pytest.mark.torch

  loader = FASTALoader(

      featurizer=featurizer, legacy=False, auto_add_annotations=True)

  data = loader.create_dataset(input_files="./data/uniprot_truncated.fasta")

  cwd = os.getcwd()

  data = loader.create_dataset(

      input_files=join(cwd, "data/uniprot_truncated.fasta"))

  assert data.X.shape == (61, 3, 5)