Fix heartbeat time glitches.
Fix heartbeat time glitches.

Without this patch you get heartbeat messages like this:

"""
[INFO] Heartbeat: During the last 22 hour(s) we saw 20 connection(s) from 2 unique address(es).
[INFO] Heartbeat: obfsproxy's uptime is 5 day(s), 0 hour(s) and 0 minute(s).
[INFO] Heartbeat: During the last 22 hour(s) we saw 20 connection(s) from 2 unique address(es).
[INFO] Heartbeat: obfsproxy's uptime is 5 day(s), 1 hour(s) and 0 minute(s).
[INFO] Heartbeat: During the last 23 hour(s) we saw 20 connection(s) from 2 unique address(es).
[INFO] Heartbeat: obfsproxy's uptime is 5 day(s), 2 hour(s) and 0 minute(s).
"""

infinity0/obfsproxy,aallai/pyobfsproxy,qdzheng/obfsproxy,NullHypothesis/obfsproxy,sunsong/obfsproxy,david415/obfsproxy,Yawning/obfsproxy,isislovecruft/obfsproxy,catinred2/obfsproxy,Yawning/obfsproxy-wfpadtools,masterkorp/obfsproxy