fix(inspec): make rubocop happy

* test/integration/default/controls/services_spec.rb: favor modifier
  if usage when having a single-line body.

* test/integration/default/controls/config_spec.rb: add frozen string
  literal comment.

* test/integration/default/controls/packages_spec.rb: ditoo.

* test/integration/default/controls/services_spec.rb: ditoo.

test/integration/default/controls/config_spec.rb

+# frozen_string_literal: true
+
 # Overide by Platform
 root_group =
   case platform[:family]

test/integration/default/controls/packages_spec.rb

+# frozen_string_literal: true
+
 # Overide by Platform
 package_name =
   case platform[:family]

test/integration/default/controls/services_spec.rb

+# frozen_string_literal: true
+
 # Overide by Platform
 service_name = 'sshd'
-if platform[:family] == 'debian'
-  service_name = 'ssh'
-end
+service_name = 'ssh' if platform[:family] == 'debian'
 
 control 'openssh service' do
   impact 0.5