use default node attribute precedence

Hey @dcrosta It seems the [Chef 11 Attributes changes](http://www.opscode.com/blog/2013/02/05/chef-11-in-depth-attributes-changes/) trigger Chef::Exceptions::ImmutableAttributeModification when the rule provider tries to set attributes without providing the precedence to use. If I simply use the default precedence this seems to work fine in Chef 11. 

Does this look cogent to you?