Fix rails version in gemspec
Fix rails version in gemspec

Changes the rails version so 4.2.0 and 4.2.1 can be used
ershad/shipit-engine,Shopify/shipit-engine,perobertson/shipit-engine,perobertson/shipit-engine,perobertson/shipit-engine,Shopify/shipit-engine,perobertson/shipit-engine,Shopify/shipit-engine,ershad/shipit-engine,ershad/shipit-engine,Shopify/shipit-engine,perobertson/shipit-engine,ershad/shipit-engine,Shopify/shipit-engine,ershad/shipit-engine