arroba.tests.test_diff.DiffTest is flaky

[snarfed]

Every now and then, maybe one run in 10, it fails with:

FAIL: test_diffs (arroba.tests.test_diff.DiffTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/ryan/src/arroba/arroba/tests/test_diff.py", line 58, in test_diffs
    self.assertEqual(100, len(diff.updates))
AssertionError: 100 != 99

Not sure if it's an actual bug or just the test itself. 😐