Fix method signature for #create_orders_shipments.
Adds tests for Bigcommerce::Api#create_orders_shipments. Fixes #64
Changed to fit 1.8 format. Fixes #64
Merge pull request #1 from sgerrand/adds-tests-on-create_orders_shipments

Adds tests for Bigcommerce::Api#create_orders_shipments
Merge pull request #65 from chriscummings/master

Fix method signature for #create_orders_shipments.