Update to match redis-py 2.10.6

[bmerry]

There are a few unit tests that fail when run against the latest redis-py (2.10.6):

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ERROR: test_set_ex_should_expire_value (test_fakenewsredis.TestRealRedis)
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Traceback (most recent call last):
  File "/home/bmerry/work/sdp/git/fakenewsredis/test_fakenewsredis.py", line 3145, in test_set_ex_should_expire_value
    self.redis.set('foo', 'bar', ex=0)
  File "/home/bmerry/work/sdp/env/local/lib/python2.7/site-packages/redis/client.py", line 1171, in set
    return self.execute_command('SET', *pieces)
  File "/home/bmerry/work/sdp/env/local/lib/python2.7/site-packages/redis/client.py", line 668, in execute_command
    return self.parse_response(connection, command_name, **options)
  File "/home/bmerry/work/sdp/env/local/lib/python2.7/site-packages/redis/client.py", line 680, in parse_response
    response = connection.read_response()
  File "/home/bmerry/work/sdp/env/local/lib/python2.7/site-packages/redis/connection.py", line 629, in read_response
    raise response
ResponseError: invalid expire time in set

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ERROR: test_set_ex_should_expire_value (test_fakenewsredis.TestRealRedisDecodeResponses)
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Traceback (most recent call last):
  File "/home/bmerry/work/sdp/git/fakenewsredis/test_fakenewsredis.py", line 3145, in test_set_ex_should_expire_value
    self.redis.set('foo', 'bar', ex=0)
  File "/home/bmerry/work/sdp/env/local/lib/python2.7/site-packages/redis/client.py", line 1171, in set
    return self.execute_command('SET', *pieces)
  File "/home/bmerry/work/sdp/env/local/lib/python2.7/site-packages/redis/client.py", line 668, in execute_command
    return self.parse_response(connection, command_name, **options)
  File "/home/bmerry/work/sdp/env/local/lib/python2.7/site-packages/redis/client.py", line 680, in parse_response
    response = connection.read_response()
  File "/home/bmerry/work/sdp/env/local/lib/python2.7/site-packages/redis/connection.py", line 629, in read_response
    raise response
ResponseError: invalid expire time in set

This is due to a change in how a zero expiry time is interpreted.