resources: fix odd require not working on 2.1

lib/shopify_api/resources.rb

@@ -1,2 +1,2 @@
 require 'shopify_api/resources/base'
-Dir.glob "#{File.dirname(__FILE__)}/resources/*", &method(:require)
+Dir.glob("#{File.dirname(__FILE__)}/resources/*").each { |file| require(file) }