time/heliocron: update to 0.6.0

[v0.6.0] - 2022-06-06
Added
  -Add --run-missed-task flag to wait subcommand (#48).
  -SleepError variant for RuntimeErrorKind. Contributed by @4e554c4c as
    part of #45.

Changed
  -Switched underlying implementation in the library from sync to async.
    Resolves #43. This adds dependencies to tokio and tokio-walltime.
    Contibuted by @4e554c4c.
  -The wait library function input arguments changed from a Duration to a
    DateTime<FixedOffset>.
  -Internal improvements to error handling.
  -Refactor tests to avoid running real wait command.

Fixed
  -Updated missing details in README.

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