Use a real gem source in Gemfile
usps api name changes fix #103 moving from matching service names (desc) to checking for service codes in order to achieve this it was necessary to override compute and retrieve rates from Spree::Calculator::Shipping::ActiveShipping::Base on Spree::Calculator::Shipping::ActiveShipping::Usps::Base I added a service code paramter to all the usps classes and made sure it was the correct id, please refer to this issue for further explanation: https://github.com/spree/spree_active_shipping/issues/103

Fixes #106