Staff scope defined in User model but not used in staff_constraint


In User model:

```ruby
scope :staff, ->{ where("moderator = 't' or admin = 't'") }
```

In lib/staff_constraint.rb:

```ruby
User.where("admin = 't' or moderator = 't'")
```

I think it would be nice to use given scopes.

If you expand the scope in User model you had also to change the value in `lib/staff_constraint.rb`.