Update dependency to spree_core 1.3.1
Make this fully work with Spree 1.3

add updateable fields to attr_accessible whitelist
Merge pull request #2 from rterbush/9a4e808db03bccdfe66afd8cc16889b7a42dabc2

More changes to support 1.3
Allow basic creation of drop_ship_orders in the admin.
Add basic ability to dispatch via drop ship orders.