Human digestible units for ETA

[aboe026]

Currently, the ETA is displayed in seconds. For large ETA (days, hours, etc), it is difficult to easily determine the time left at a glance due to having to convert the seconds to an appropriate unit in the user's head. It would be much nicer if the ETA displayed in units greater than seconds when appropriate (for example: "1m22s"). See https://github.com/aboe026/ci-cd/blob/master/src/backup.ts#L222 for an implementation.