2 2 stable

I'm getting a NoMethodError due to nil.(:>, 0).

Using `is_package_shippable?`  inside `available?` fixes missing `is_package_shippable?` call inside `compute_package` of `Spree::Calculator::Shipping::Usps::PriorityMailInternational`

If this was left out for a specific reason, would you be kind explaining me why?