Here's my first pass at getting the code to pass all rubocop citations.

xkcd_passphrase.rb

#!/usr/bin/ruby

require 'net/http'
require 'nokogiri'
require 'rss'
require 'open-uri'

google_news_query = 'http://news.google.com/news/feeds?q=apologize&output=rss'
google_news_result_url = ''
wordlist = []

open(google_news_query) do |rss|
  feed = RSS::Parser.parse(rss)
  item = feed.items[0]
  google_news_result_url = item.link
end

doc = Nokogiri::HTML(open(google_news_result_url))

all_words = ''
doc.traverse{ |node|
  if node.text? and not node.text =~ /^\s*$/
    all_words << node.text
  end
}
wordlist = all_words.split("\s")
wordlist.reject!(&:empty?)
wordlist.each { |word| word.gsub! /\W/, '' }

random_output = ''
random_data = open("http://www.random.org/integers/?num=4&min=0&max=#{wordlist.length}&col=1&base=10&format=plain&rnd=new") { |data|
  generated_number = data.read
  random_output << generated_number.chomp
}
random_numbers = random_output.split(/\s/).map(&:to_i)
puts "#{wordlist[random_numbers[0]]} #{wordlist[random_numbers[1]]} #{wordlist[random_numbers[2]]} #{wordlist[random_numbers[3]]}"

Hmm. Okay, this is going to take some deeper hacking to get it to work. Sigh....