feat(currency-rates): update once every day to reduce quota usage

* Currently we are using too many API calls

backend/cron_tasks.py

@@ -25,7 +25,7 @@ logger = logging.getLogger("django")
 
 
 # @timer(60, target="spooler")  # use this for tests
-@timer(3 * 60 * 60, target="spooler")  # run it three hours
+@cron(5, 0, -1, -1, -1, target="spooler")  # everyday at 5 past midnight
 @harakiri(40)
 def _update_currencies(num):
     update_currencies()