Fix platform/arch

Author: HD Moore

modules/exploits/multi/http/rails_xml_yaml_code_exec.rb

@@ -35,8 +35,8 @@ def initialize(info = {})
 					['CVE', '2013-0156'],
 					['URL', 'https://community.rapid7.com/community/metasploit/blog/2013/01/09/serialization-mischief-in-ruby-land-cve-2013-0156']
 				],
-			'Platform'       => [ 'ruby'],
-			'Arch'           => [ 'ruby'],
+			'Platform'       => 'ruby',
+			'Arch'           => ARCH_RUBY,
 			'Privileged'     => false,
 			'Targets'        =>	[ ['Automatic', {} ] ],
 			'DisclosureDate' => 'Jan 7 2013',