Fix a typo in the directory spec where cache was used instead of client

   consensus is no longer fresh, and 7/8 of the time remaining after

   consensus is no longer fresh, and 7/8 of the time remaining after

   that before the consensus is invalid.)

   that before the consensus is invalid.)

   [For example, if a cache has a consensus that became valid at 1:00,

   [For example, if a client has a consensus that became valid at 1:00,

    and is fresh until 2:00, and expires at 4:00, that cache will fetch

    and is fresh until 2:00, and expires at 4:00, that client will fetch

    a new consensus at a random time between 2:45 and 3:50, since 3/4

    a new consensus at a random time between 2:45 and 3:50, since 3/4

    of the one-hour interval is 45 minutes, and 7/8 of the remaining 75

    of the one-hour interval is 45 minutes, and 7/8 of the remaining 75

    minutes is 65 minutes.]

    minutes is 65 minutes.]