rubocop: disable Style/RegexpLiteral

this cop doesn't make much sense in our spec file. the regex delimiter
would be {}, but we often have to test for these braces.

spec/classes/unattended_upgrades_spec.rb

@@ -1,5 +1,6 @@
 require 'spec_helper'
 
+# rubocop:disable Style/RegexpLiteral
 describe 'unattended_upgrades' do
   let(:file_unattended) { '/etc/apt/apt.conf.d/50unattended-upgrades' }
   let(:file_periodic) { '/etc/apt/apt.conf.d/10periodic' }