Fix a Mongoid spec by switching the rule creation order in it

**Merging into: ryanb:2.0**


Specific rules overrule/exclude generic rules and should therefore be defined first if both rules need to be evaluated.

An actual use case would be:

```` ruby
user.can :read, :documents, :user_id => user.id
 
if user.admin?
  user.can :read, :documents
end
```` 

`relevant_rules # => [:read, :documents], [:read, :documents, {:user_id => user.id}]`

and the following would then not work, because of the `specificity` rule.
Given, `user.admin? #=> true`:

```` ruby
if user.admin?
  user.can :read, :documents
end

user.can :read, :documents, :user_id => user.id
```` 

`relevant_rules # => [:read, :documents, {:user_id => user.id}]`