def -(other)
      d = ::ROS::Duration.new
      d.secs = @secs - other.secs
      d.nsecs = @nsecs - other.nsecs
      d.canonicalize
    end
def -(other)
      d = ::ROS::Duration.new
      d.secs = @secs - other.secs
      d.nsecs = @nsecs - other.nsecs
      d.canonicalize
    end
subtract time value.
 @param [Time] other
 @return [Duration] duration