update file name format to avoid issues with saving files with some systems
update file name format to avoid issues with saving files with some systems

have seen these earlier with a name like bulk-payloads-2018-02-20 16:42:54.488399 having issues with : in file name
dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq