Pre-emptively deal with require issues.

Basically, when anyone else made a 'resource_override' generator,
it'd only require once. Because that's how require works. So let's make
sure that we require ours and nobody else's.

See rails-api/active_model_serializers@2edaa22

lib/draper/railtie.rb

@@ -6,7 +6,7 @@ class Railtie < Rails::Railtie
       app ||= Rails.application # Rails 3.0.x does not yield `app`
 
       Rails::Generators.configure! app.config.generators
-      require 'generators/resource_override'
+      require_relative 'generators/resource_override'
     end
   end
 end