Fix rubocop and kitchen complaints (see full msg)

.rubocop.yml - AllCops/Excludes was renamed to AllCops/Exclude

Warning: Deprecated pattern style 'vendor/**' in .rubocop.yml. Change to 'vendor/**/*'.

metadata.rb:1:5: C: Put one space between the method name and the first argument.
name             'xml'
    ^^^^^^^^^^^^^
metadata.rb:2:11: C: Put one space between the method name and the first argument.
maintainer       'Opscode, Inc.'
          ^^^^^^^
metadata.rb:4:8: C: Put one space between the method name and the first argument.
license          'Apache 2.0'
       ^^^^^^^^^^
metadata.rb:5:12: C: Put one space between the method name and the first argument.
description      'Installs xml'
           ^^^^^^
metadata.rb:7:8: C: Put one space between the method name and the first argument.
version          '1.2.5'
       ^^^^^^^^^^
attributes/default.rb:24:32: C: %w-literals should be delimited by ( and )
  default['xml']['packages'] = %w[libxml2-devel libxslt-devel]
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
attributes/default.rb:26:32: C: %w-literals should be delimited by ( and )
  default['xml']['packages'] = %w[libxml2-dev libxslt-dev]
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
attributes/default.rb:28:32: C: %w-literals should be delimited by ( and )
  default['xml']['packages'] = %w[libxml2 libxslt]
                               ^^^^^^^^^^^^^^^^^^^
[COOK-4651] Pin nokogiri at a working version

The xml community cookbook has a dependency on nokogiri [1]. However, nokogiri just did a new release [2], and it uses a new version of mini_portile [3], which has a brand new dependency on 'git apply' being a working command.

I have notified the nokogiri project [4], but I also think it's important to pin the xml cookbook to known working versions of dependencies (instead of 'any nokogiri version you can find').

[1] https://github.com/opscode-cookbooks/xml/blob/master/recipes/ruby.rb#L35
[2] https://groups.google.com/forum/#!topic/nokogiri-talk/dPtmByhszRA
[3] https://github.com/luislavena/mini_portile/issues/32
[4] https://github.com/sparklemotion/nokogiri/issues/1102
Merge upstream. Attribute for version was introduced. I argue we should default it to a known working version of nokogiri.
Merge pull request #13 from martinb3/COOK-4651

[COOK-4651] pin nokogiri to a working version