Easiest solution for vuln string

Signed-off-by: imjoseangel <josea.munoz@gmail.com>

Author: imjoseangel

controls/os_spec.rb

@@ -253,7 +253,7 @@
 
     loaded_files.each do |vulnfile|
       describe file(vulnfile) do
-        its('content') { should_not match /vulnerable/ }
+        its('content') { should_not match 'vulnerable' }
       end
     end
   end