Fix service pack parsing

Author: HD Moore

modules/post/windows/gather/enum_ad_computers.rb

@@ -108,8 +108,8 @@ def run
               if field.to_i > 0
                 report[:os_sp] = 'SP' + field
               end
-              if field =~ /(Service Pack|SP\s?)(\d+)/
-                report[:os_sp] = 'SP' + $1
+              if field =~ /(Service Pack|SP)\s?(\d+)/
+                report[:os_sp] = 'SP' + $2
               end
 
             when 'description'