Use new "strong parameters" from rails4

spec/models/user_spec.rb

@@ -9,7 +9,6 @@ describe User do
   it { should validate_presence_of :email }
   it { should validate_presence_of :password }
   it { should validate_presence_of :password_hash }
-  it { should_not allow_mass_assignment_of :password_hash }
 
   context 'when a user with the same email address already exists' do
     let(:old_user)  { FactoryGirl.create(:user, email: 'unique@example.net') }