Should parse ISO8601 microsecond timestamps

[kenaniah]

Chronic.parse "2018-05-24T15:43:09.5582332-05:00" #=> nil
Chronic.parse "2018-05-24T15:43:09.559-05:00" #=> 2018-05-24 15:43:09 -0500

It appears as though chronic refuses to parse anything more precise than milliseconds, as evidenced in the first result.