Update dependencies

Hi guys,

A bunch of rather outed gems prevent us from using Spree.
While updating ```kaminari``` and ```cancancan```, updating ```ransack``` caused two failures in https://github.com/StupidCodeFactory/spree/blob/master/backend/spec/features/admin/products/products_spec.rb which i have fixed.
Let me know if something is wrong.

**CHANGES:**
* updated kaminari, cancancan and ransack
* fix product admin page:
  delete 'deleted_at_null' from the search query hash as now ransack behaves
  properly and won't include products with null delete_at value