minor refactor of json_task.py to address issues 561 and 562 (#568)
minor refactor of json_task.py to address issues 561 and 562 (#568)

Co-authored-by: Ambrose Slone <c72f03c2b843b0269754277bf2b510fa15fae635@google.com>
google/BIG-bench,google/BIG-bench