sync fails when issues change during iteration

[soundofjw]

Iterating over issue_tasks fails when the set changes, which occurs during the sync process.

Traceback

Exception: RuntimeError('Set changed size during iteration',)
Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/asana_hub/tool.py", line 401, in __init__
    action.run()
  File "/Library/Python/2.7/site-packages/asana_hub/actions/sync.py", line 278, in run
    for task_id in issue_tasks:
RuntimeError: Set changed size during iteration

Asana Tasks:

#42615941001493