Log Message:
Updated p5-Date-Manip to 6.60.

Bug fixes

Fixed a bug where if a recurrence had no interval, start and end dates passed
in to the dates method would not work.  PJ-DSI-DevOps (GitHub #12).

Documentation fixes

Clarified Date::Manip::TZ::all_periods.  Based on discussion with
Peter Pfannenschmid.