Adjust direction page cache timeout from 36h to 4h

The direction page cache is currently set to a 36 hour timeout as per #958 (closed) / !12065 (merged). This update proposes changing the timeout to 4 hours to make a one day iteration workflow more realistic. At the moment, doing iterations on issues for the direction page is challenging because you need to wait 36 hours for the changes to be reflected in review apps. One original suggestion from @sytses in the issue was to set the cache expiry to 3 or so hours.

Performance

For reference, the performance impact of running direction.rb was measured as follows on my local machine when 100% of requests were cache misses:

real    4m42.037s
user    0m1.609s
sys     0m0.531s

During this time, it makes 217 GET requests:

Jasons-MacBook-Pro-2:generators jlenny$ cat out.txt |grep -o 'request: GET' |wc -l
     217

cc @markpundsack @rspeicher @stanhu @JobV