Tests fail on python 3.7

[eli-schwartz]

Arch Linux is currently trying to update to python 3.7.0, and while rebuilding all packages in our repositories, pcapy failed the testsuite with the following log:

======================================================================
FAIL: testEOFValue (__main__.TestPcapy)
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Traceback (most recent call last):
  File "pcapytests.py", line 52, in testEOFValue
    self.assertEqual(refNone, sys.getrefcount(None))
AssertionError: 5918 != 5915

----------------------------------------------------------------------
Ran 6 tests in 0.002s

FAILED (failures=1)

I am experiencing the same issue in 3.7.0