Erlang/OTP でもう時間に苦労しなくていいんだ！
> calendar:system_time_to_rfc3339(erlang:system_time(second)).
"2019-10-07T22:29:02+09:00"> calendar:system_time_to_rfc3339(erlang:system_time(second), [{offset, "+09:00"}]).
"2019-10-07T22:29:36+09:00"> calendar:system_time_to_rfc3339(erlang:system_time(millisecond), [{unit, millisecond}, {offset, "+09:00"}]).
"2019-10-07T22:30:58.547+09:00"> calendar:system_time_to_rfc3339(erlang:system_time(millisecond), [{unit, millisecond}, {offset, "Z"}]).
"2019-10-07T13:38:32.376Z"> calendar:system_time_to_rfc3339(erlang:system_time(microsecond), [{unit, microsecond}, {offset, "Z"}]).
"2019-10-07T13:39:17.188199Z"
