RecurringApplicationCharge cannot update the usage cap to a decimal amount

[umsu2]

func (r *RecurringApplicationChargeServiceOp) Update(chargeID, newCappedAmount int) (
	*RecurringApplicationCharge, error) {

	path := fmt.Sprintf("%s/%d/customize.json?recurring_application_charge[capped_amount]=%d",
		recurringApplicationChargesBasePath, chargeID, newCappedAmount)
	resource := &RecurringApplicationChargeResource{}
	err := r.client.Put(path, nil, resource)
	return resource.Charge, err
}

the newCappedAmount should be the type decimal instead of an int.
however the change would be break the original interface.

[oliver006]

Addressing this in #258

[oliver006]

v4.0.0 was released - this should be fixed.