fix(rubocop): add fixes using `rubocop --safe-auto-correct`

test/integration/default/controls/config_spec.rb

@@ -1,12 +1,14 @@
+# frozen_string_literal: true
+
 control 'AptCacherNG configuration' do
   title 'should match desired lines'
 
   describe file('/etc/apt-cacher-ng/zzz_acng.conf') do
     # Default config
-    its('content') { should include "BindAddress: 0.0.0.0" }
+    its('content') { should include 'BindAddress: 0.0.0.0' }
 
     # Custom config
-    its('content') { should include "Port: 9999" }
+    its('content') { should include 'Port: 9999' }
   end
 
   describe file('/etc/apt/apt.conf.d/80proxy') do

test/integration/default/controls/package_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 control 'AptCacherNG package' do
   title 'should be installed'
 

test/integration/default/controls/service_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 control 'AptCacherNG service' do
   title 'should be running and enabled'