Update rails to 4.0:

* Add protected_attributes gem dependency;
* Remove deprecated usages of AR .find method;

spec/models/track_spec.rb

@@ -15,6 +15,8 @@ describe Track do
       track.file = file
     end
 
+    it { should be_valid }
+
     it 'creates a sound for the track' do
       expect {
         track.save