tests.spider::test_generator fails sometimes

[lorien]

https://travis-ci.org/lorien/grab/jobs/375132058#L844

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FAIL: test_generator (tests.spider.BasicSpiderTestCase)
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Traceback (most recent call last):
  File "/home/travis/build/lorien/grab/tests/spider.py", line 93, in test_generator
    self.assertEqual(bot.stat.counters['count'], 1111)
AssertionError: 1107 != 1111