uninitialized constant Resque::Failure::Multiple

I was setting this up in a `resque.rb` initializer in my Rails app and was getting an `uninitialized constant Resque::Failure::Multiple` error using the current setup instructions. 

I needed to add a `require 'resque/failure/multiple` to get it to work, which I found here: https://github.com/defunkt/resque/wiki/Failure-Backends