test failure: dir_handle_get/status_vote_next_bandwidth

Found by travis: https://travis-ci.org/torproject/tor/jobs/515199996

dir_handle_get/status_vote_next_bandwidth: 
  FAIL src/test/test_dir_handle_get.c:2535: assert(strstr(header, expires))
  [status_vote_next_bandwidth FAILED]

To me this looks like a race condition: the clock probably has advanced by a second between the call to directory_handle_command_get() and the call to time(NULL).