Update model.js

[luiztools]

Modern Sequelize doesn't have findById anymore, so, we need to change this to add support to findByPk function.

[tawfiknasser]

I agree that we need to support findByPk and it should replace it. but this is another functionality.
primary key is not always id. Pk column can be called in many names (id, UUID, ID).

also we need to refactor the tests if we are changing the function name.