Lcg/chef 12 attr

See https://gist.github.com/danielsdeleo/da9a8d9a91cc8c2781b0
so that means if we're deleting `node['foo']['bar'][5]['baz']` which will be called as node.rm('foo', 'bar', 5, 'baz') then the attr object will wind up an array and we'll hit it with '[5]' which is valid for it -- so it seems like this works?

i can write some specs with arrays...