test_sortKeys (__main__.UltraJSONTests) ... Fatal Python error

[cdluminate]

As mentioned in #206

1.35 didn't fix the problem for python 3.6:

test_sortKeys (__main__.UltraJSONTests) ... Fatal Python error: ./python/objToJSON.c:934 object at 0x7f89ab0cab48 has negative ref count -1

Current thread 0x00007f89ad62c740 (most recent call first):
  File "tests/tests.py3", line 931 in test_sortKeys
  File "/usr/lib/python3.6/unittest/case.py", line 605 in run
  File "/usr/lib/python3.6/unittest/case.py", line 653 in __call__
  File "/usr/lib/python3.6/unittest/suite.py", line 122 in run
  File "/usr/lib/python3.6/unittest/suite.py", line 84 in __call__
  File "/usr/lib/python3.6/unittest/suite.py", line 122 in run
  File "/usr/lib/python3.6/unittest/suite.py", line 84 in __call__
  File "/usr/lib/python3.6/unittest/runner.py", line 176 in run
  File "/usr/lib/python3.6/unittest/main.py", line 256 in runTests
  File "/usr/lib/python3.6/unittest/main.py", line 95 in __init__
  File "tests/tests.py3", line 959 in <module>
Aborted