fix a deprecation warning in rails4

flag_shih_tzu works fine on rails 4 beta1 but there is that annoying deprecation warning about the  scope, This pull request fixes it.

    DEPRECATION WARNING: Returning a hash from a #scope or #default_scope block 
    is deprecated. Please return an actual scope object instead. 
    E.g. scope :red, -> { where(color: 'red') } 
    rather than scope :red, -> { { conditions: { color: 'red' } } }. 
    (The scope was defined at (eval):1.).