Avoid scope error in tests (Mongoid 4)

Mongoid 4 throws the following errors when running specs. This PR only modifies the specs/non-lib files to fix it. Verified it works on Mongoid 3 as well.

* Issues with loading Mongoid Paranoia gem (have also changed to using official release version of Mongoid Paranoia)
* Scopes must be procs on Mongoid 4

   ```
   /lib/mongoid/scopable.rb:306:in `check_scope_validity':  (Mongoid::Errors::InvalidScope)
   Problem:
      Defining a scope of value #<Mongoid::Slug::Criteria:0x4195c20> on Page is not allowed.
   Summary:
     Scopes in Mongoid must be procs that wrap criteria objects.
   Resolution:
     Change the scope to be a proc wrapped critera.
   ```