Update link to API docs
Update link to API docs

Shopify redirects api.shopify.com to docs.shopify.com/api
resistorsoftware/shopify_api,aareano/shopify_api,carsonreinke/shopify_api,ipmobiletech/shopify_api,discolabs/shopify_api,kevinmpowell/shopify_api,DanielVartanov/shopify_api,cefigueiredo/shopify_api,lalithr95/shopify_api,kingscott/shopify_api,Shopify/shopify_api