v1.60.0

• Add unpadded %H, %M, and %u format directives to Duration#format for
  unpadded hours, minutes, and seconds, complementing the existing zero-padded
  %h, %m, and %s
• Update the directive regex in format from /%[DdhmSs%]/ to
  /%[DdHhMmuSs%]/ to match the new directives