Fix test_filename_filtering test (#1647)
Fix test_filename_filtering test (#1647)

CI tests fail with:

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FAIL: test_filename_filtering (gensim.test.test_corpora.TestTextDirectoryCorpus)
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Traceback (most recent call last):
  File ".../lib/python3.6/site-packages/gensim/test/test_corpora.py", line 462, in test_filename_filtering
      self.assertEqual(expected, filenames)
      AssertionError: Lists differ: ['/tmp/tmp0j1tou_7/test1.log', '/tmp/tmp0j1tou_7/test2.log'] != ['/tmp/tmp0j1tou_7/test2.log', '/tmp/tmp0j1tou_7/test1.log']

It's not a real failure, since the files are correct, only their order of
comparison is not same
mattilyra/gensim,mattilyra/gensim,RaRe-Technologies/gensim,markroxor/gensim,mattilyra/gensim,gojomo/gensim,piskvorky/gensim,gojomo/gensim,RaRe-Technologies/gensim,RaRe-Technologies/gensim,gojomo/gensim,piskvorky/gensim,markroxor/gensim,markroxor/gensim,piskvorky/gensim,RaRe-Technologies/gensim,gojomo/gensim